I could tell you what I USED to do, to get in the best shape of my life...
 When I started taking Martial Arts (Wing Chun),  the school had a 1hr hardcore "Core" workout routine, before
any other lessons / drills were performed.
 Starting with some basic Stretches:
- Head Rolls:  Roll your head in clockwise circles for a 5 or so seconds,  then in the Opposite direction 5 sec.
- Forward Stretch:  Breath in fully, slowly exhale.. as you reach towards you Toes, stretching your back (maybe 3 min)
- Back Bend:  Wide stance, and Lean backwards.  Keep relaxed, allowing a gradual further bend,
while breathing nonstop (maybe 2-3 min)
 (Briefly Lean forwards once more, to relive any stress and strain)
- Shoulder Stretch:  Cross an arm across your body horizontally.  Use your other arm to pull it towards
your body tightly..  and hold for several seconds.  Repeat on the other arm.
- Arm Rotations (windmills):  Rotate Both arms vertically on both sides of your body at the same time.
Forwards for about 60 sec. Backwards 60 sec.
- Backwards Shoulder Stretches:  Starting at belly button height, and both palms facing forwards... quickly jerk your
arms backwars, until they cant move any further, causing a stretch to you shoulders and pecks.  Then move your
arms up about 6 inches, and repeat.  Keep going higher each time, until your arms are directly over your head..
Then work your way back down.  Keep at this, for about 3 min.  This is a good "Range Of Motion" stretch.
- Wrist Rotations:  Extend a single arm in front of you... fully locked out, with your palm facing the ceiling.
Place your other arms palm under your extended arms Elbow, to support it. Keep your arm at shoulder
level, static in place... at all times.   Bend your wrist towards your body (without bending the fingers), and then
rotate your wrist/fingers in a circle towards the floor, then back upwards... until your fingers are pointing
back up to the ceiling.  Make sure to keep inwards pressure at all times, while rotating.  Repeat these circles
for about 1 min, then rotate in the opposite direction for another min.  Shake your arm and fingers loose.. then
swap arms, and repeat the same thing.
- Body Twists:  Cross your arms in front of your chest, with both hands resting on each forearm, near the elbows.
Semi wide stance.  Keep your arms and upper body, locked together, as you rotate to the left.. as far as your body
will rotate.  Then rotate to the right, until your body stops.  Keep rotating side to side, as Quickly as possible,
while also trying to extend the Rotation further each time... for about 3 min.  Do not stop at any time.. its a
nonstop stretch, combined with a Speed (acceleration) Drill.  Breaths have to be quick and shallow. Exhale out
the nose as you twist left.. In the nose as you return to center.. out the nose as you twist right, in as you return
to center... etc.
Now on to the main Exercise portion:
- Three Sets of Special Pushups:
A)   Slow Motion, Barefist, Wing Chun Pushups
   1) Make two  "Thumbs Up"  signs with your hands.  Bring them together, so that your thumbs are touching, and your
wrists + knuckles are touching.  The thumbs up will add some Support.
  2) Place your Wristbones in the center of your chest, between your Moobies (sternum)
  3) Place your fists on the floor, with arms locked fully out.. and your Sternum should ALWAYS remain directly over
your Fists at ALL TIMES.  Its easy to accidentally move your body diagonally, when raising / lowering.
  4) Your feet and ankles should be Touching together... at all times.  No wide open legs.  No separating your ankles
during your sets.
  5)  Breath In fully through the Nose.  Start to Lower yourself slowly.. as you slowly Exhale out the Mouth.  It
should take you anywhere from 7 to 12 seconds, depending on your skill level, and the length of your arms.
The Slower the Better + Quicker your Triceps build results.
You want to keep both arms sliding across your ribcage, at all times.  You DONT want your elbows away from your
body like "Wings".   Keep them tightly to your body (but any without inwards forced strain.  We call this the
Elbow Down position.. as the elbows are pointed towards the feet)
6) You want to lower yourself until the center of your chest touches the tops of your wristbones.  Make sure to ALWAYS
make physical contact, before raising.  SLOWLY breath inwards through the nose, as you SLOWLY raise back
upwards.  Your pace and speed should be even and controlled... and take the same amount of seconds as
you lowered (same timings for the entire exercise).   At the top, your lungs SHOULD be completely full
(if your timings are off, you may breath fully now... before lowering again).
Because your arms are in the CENTER of your body.. your body will be Higher off the ground.. meaning a much
LONGER vertical travel.  This will develop much more of your arms, than a standard pushup.  It will also feel
much more straining..  closer to that of a single arm pushup, in difficulty. Being centered also means you have
to keep your body "Balanced" at all times... which will create additional work / strain.
Because these are done much Slower... you will have no way to do typical "Momentum Cheats".  As such, you will
find these much more challenging, as well as will develop much greater strength.. all along the ENTIRE pathway,
from chest to full arm extension.
If you were to Stand up, and perform one in the air.. you would see that its the same movement as a
Vertical Fist Punch.  As such, it develops real world Punching Strength... Using any hand strikes, or pushes,
that drive forwards.
7) Three Sets of 15, for Beginners.  You want at least 15 of these per non-stop Sets.  No rests in the middle of
a set.  Just keep pushing... even through your muscles, and or knuckles, may be Screaming at you.

 Rests:  After a set.. roll your arms in a few large circles... forcing the blood back into the arm and fingers.
Then shake, flex, and move your fingers around, for a few sec.   Rest for about 2 min., before starting
the next Set
9) Set Variances:   While you should always have at least ONE Set dedicated to a slow vertical fist set...
You may also want to randomly add some other sets and methods, on the other two sets.
Variant A - DOWN SLOW + UP FAST.   Rather than both directions being slow.. adding an Explosive Speedy
burst upwards.. trains your Explosive Power (speed / acceleration + power).
Variant B - Down Slow + Up Fast + Hop.   When swiftly rising, you can push your fists into the air... and even
add in a clap or two if you want, before dropping back on your knuckles.
Standards Fast Pushups.  Typical wide arm pushups.. done as fast as possible.  You will want to raise the number
on these, to something like 50 or +100, for a single Set.
Diamond Pushups.  Make a Triangle shape with your hands, connecting your thumbs and pointer fingers.
Rather than starting at the center of your chest.. you want to extend your arms further in front of your body...
so that the Triangle is slightly in front of your head.  Maybe 6 inches or more, ahead of your head.
As you lower yourself, you want to drop down in a way... that the center of your forehead ends up in the
center of the triangle.
Typically, 1st Set was Slow+Slow verticals.  Next Slow+FAST verts  OR  50 to 100 Standard fast pushups.  
End Set was Diamonds.
Next Up... is the Abdomen work...
 Three Sets of Crunches:
1)  30 to 50 Standard Crunches
2)  Rest about 2 min, before next Set
3)  Twisting Crunches.  Directing your elbows towards your opposite Knees, as you rise
4)  HOLDS.  Rise up into a Crunch.. but remain in the air, with your Abs tightened... for a certain
amount of time.  Maybe 10 seconds.  Sink to the floor, and relax for 3 to 5 sec... then Up again,
into a 10 sec hold.   Repeat this process for anywhere from 8 to 12 reps.
 Next is Lower Abs, via Leg Spins, Leg Raises, and Leg Holds:
1)  Make a Triangle shape with your hands, and while on your back.. place the end of your spine, in
the center of that triangle.  Your butt cheeks will be sitting on the backs of your hands, with your spine
raised and protected from grinding heavily on the Floor.
2)  Extend both of your legs out.. with your toes pointed towards you head (at all times).  Both your Feet
/ Ankles should be Touching.. at ALL times.
3)  Slowly Raise your locked out Legs into the air.. so that the heels of your feet are 6 inches from the
floor.
4)  Circles:  Keeping your toes pointed towards upwards, move your legs in a circle, about the diameter
of a Basketball.  Keep the pace of your circles at a medium slow pace... and make sure to TRY to keep
the Shape of your circles "Even" in shape, and approximately the same diameter.
5)  Start the Count at 10 Circles Clockwise.  Then without setting down, 9 Counter-Clockwise circles,
then 8 Clockwise circles..  etc... until you have completed the final 1 circle.
 DO NOT SET your feet down for the ENTIRE duration of this Exercise !!!  (should be like 3 to 5 min)
6)  After the Circles... Immediately go into SLOW leg lifts.  Raise both legs slowly upwards, maintaining
a slow and steady pace.. until they are at or nearly 90 degrees.  Now slowly Lower them at the same
speed / pace, until they are 6" from the floor.  Repeat this while breathing properly... for maybe
3 to 5 sets... 
7)  Now keep one leg 6" from the ground.. and ONLY raise the Opposite leg, slowly into the air.. which
keeping the other leg, exactly where it is.  Lower the leg, then swap the roles of each leg.  Repeat this
maybe 4 times minimum (two leg lifts per leg).
8 )  Another slow set of BOTH Legs up and down... maybe 3 more times.
9 )  Once back to center... and still 6" off the Ground... Hold your legs STATIC, for anywhere from
30 to 60 seconds (extend times as you get better).
10 )  Slowly Lower your feet back to the floor, and rest.
 This was the main set of Exercises.   The final thing we did, were some partner Leg Stretches, 
and a final Cool-Down, which was a sort of Brief  "Meditation", where you just Calm your thoughts,
heartbeat, etc.. down, while sitting indian style, with your eyes closed.  That was about 5 min.
 That said... Randomly During classes, we would be asked to do various other Exercises, like a set
of Burpees.  Or a 60 second non-stop "Speed Drill".   Or something like a 20 minute
nonstop partner drill  (punches + deflections).   Or standing on one Leg.. while slowly extending and
retracting your kicking leg.. for 2 to 3 minutes per leg (repeated twice per leg).
 And or something like Hitting the wall mounted Sandbags, barefisted, for anywhere from 15 min,
or to the End of class.
 At that Time, I was attending school 4 days a week.. 2 hrs per class.  I was biking there and back,
which was about 30 min each way.  And when I was between jobs... I took both the Day, and Night
classes.  Same exact class material.. but just more time and effort devoted to progression / mastery.
 I was also repeating the same workout at home, every single day of the week... on top of other
training at home, or outside of classes, elsewhere.  For example.. standing on one leg while waiting
in long lines at the bank/stores.  Throwing hand techs, and kicks.. randomly, all throughout the entire
day / night... no matter where I was... maybe every 15 mins.  Even at work, in the backroom.  Even
at the mall, while walking in public.  I didnt care what anyone thought.  I only cared about faster
progression and mastery.
 I would later add various other training into the mix.  Getting a Kick bag, for round / high kicks.
And do other exercises, like Inverted Handstand pushups.. while against a wall.
 At one point I had a teacher (ive had 3 different teachers over the years) reveal the
Slow Motion Form work, which takes a little over 1 hour per session.  This "Internal" training, was
a lot more challenging than one would imagine.  I did that every other day, for a consecutive
3 months or so... and developed some Crazy changes to my mind and body.  Most especially,
a much greater level of Tendon Strength... and an expanded level of Bodily Awareness, and
3d Spatial Awareness.  My movements also became like a "Surgical" level of Precision. Accuracy
down to within 2 to 3 mm... even at full combat speeds.
 Anyway.. I believe I went from a 31" waist.. with about 140 to 145 lbs.. to about 150 lbs, with a
32" waist.. within about 6 months (maybe a year.  I really cant recall), of that pace and intensity.
It was the first time in my life, that I was starting to pack on some actual muscle, and mass.
I was also noticing some actual Muscular Definition, showing up.  Especially the legs and triceps.
And my Core Strength, was insane.  I went from having a Jello Soft belly.. to having Rock hard
abs.
 I believe by my 5th year, I was about 165 to 175 lbs. (at 6ft tall).  I was no longer an Under-Weight
Stick Figure.  I was a solid and dense beast.   Mind you.. I started out in school, as the kid that got
picked last in Gym classes... due to how poorly coordinated I was.. and how weak + Frail I was.
 I went from being slow, clumsy, frail and weak..  to being Lightning Fast, Graceful as a Cat, Powerful
as a Lion, Able to take a heavyweights hits without serious issues, and had developed real world self
defense skills.. that Id tested and proven against much larger and stronger blackbelt level fighters..
from various other local schools.
 So, my advice to anyone thats still Capable of a Decent level of Exercise... is to join a Martial Arts
school... as well as to do a Core workout at home, as a minimum.   The martial arts makes workouts
more "Fun"... and so you tend to stick with it.   Arts like Tae Kwan Do... burn a lot of calories,
while also developing great leg skills... all without needing to go full hardcore combat levels of fighting.
If you want more Serious level of combat training.. arts like Muay Thai... add in the necessary
Shin, Bone, and Body Conditioning.  You will find even more Radical Conditioning, in Arts like Shaolin,
where they do full body Iron Body conditioning (which also includes soft tissue areas, like the Throat).
Kickboxing is a decent starter too... that also burns a lot of Calories.  I recommend staying away from
the more complex arts, until one has developed a decent level of Strength, Fitness, Toughness,
and basic coordination.  Basically, develop good foundations first, then add the more challenging
technical skills.. later.