I've got about 30 months deployed, plus about 18 months worth of field time/training spent away from home in the last decade and a bit. Been married through all of it to the same gal. Trick is that there is no trick. It's about community, it's about making communication a priority, it's about knowing that if it's broke time apart isn't going to make it better so fix it before you leave, it's about expectation management when you return home.
Things are different everyday. When you're there everyday the changes are gradual so you feel it as the same. When you pop off for a few months or a year+ you get hit in the face with that change all at once when you get home. The both of you grow every day. Just because you're not together doesn't mean you're growing apart tho.
My wife and I are used to separations, we know how to deal with it, and we know how to handle reunions. That's a leg up - if you and the missus don't spend a lot of time apart it can be hard to reconnect or stay connected. It's a skill you two may not have had to cultivate. Something to keep in mind.
Oh, and keep it in your pants. Nothing kills a marriage faster than herpes.