I'm in total agreement with mtd and JustMichael:
#1) Plan, plan, plan, plan, plan. Then... plan some more.
Spend a lot of time circling the cabinet, measuring, taking notes, sketching out plans... Visit Home Depot (a lot!), look at everything and ask, 'can I use this? How would I use this?' Spend hours here reading the forums and looking at others projects.
#2) Finish the CP last, or at least assemble the CP and affix it last. I almost followed this rule.. My cabinet was almost 100% finished. The only thing left to do was find a good spot for the power button. Two years later and I FINALLY took care of that, after two years of bending over and grabbing hold of a button hanging off of a wire coming out of the coin door.

I definitely recommend planning the control panel first, though. First, decide what controls you want. What types of joysticks, how many buttons, spinner, trackball, etc... Then order all of the parts, take measurements of them, and do a mockup on cardboard. Install the buttons on that cardboard and everything. I don't really feel a need to hook it up to a pc at this point, but pretend to play it, visualize the various games etc.
I spent a lot of time on this, more than anything else, and it really paid off. No redrilling, redoing a CP. What I found easiest to do is either print out the exact size of things w/ a cad program, or sketch them out. Then I cut out the buttons and taped them to another sheet of paper in the configuration I decided on (6 buttons each joy), 'pretended' to press them, and kept reaffixing them (closer, farther apart) until I was most confortable, then photocopied that config. Then I sketched the size of the joystick and affixed it to my button config, photocopied it twice, cut them out. I did my various other controls in the same way (asteroids buttons, trackball buttons, etc), cut out each mockup and taped them to a piece of cardboard in the most comfortable layout, installed the buttons for better verification, and made sure I build the frame for my control panel to that size.
I feel that it's much better to decide on the size of the control panel this way than to decide on a size first and have to cram everything into it. (Unless you are doing modular panels/keeping to the exact dimensions of the original panel.)
Phew... can anyone tell I tend to talk a lot?
