The best advice I can give you is when you are coming up on retirement start thinking of all the things that have happened to you medically over your career. Even minor stuff, start listing it somewhere. And if it happened when you were 'off duty', still put it in (rugby injury on a weekend, put it in!). When you get to your seperation/retirement physical don't hold anything back, mention everything! Also, make several copies of your medical records so that when they get lost, you aren't screwed.
When it finally comes time for you to actually seperate (And you have completed your seperation physical), contact some of your local veteran service organizations and see what kind of help they provide filling out the disability form. Here in DC the DAV helps with most of the cases. The service organizations have people trained specifically to help you fill out the forms (they don't do it for you but are a huge help). They even review your medical records and point out things you might want to put in for. You can do this while you are still on active duty, about to seperate/retire. There is also a pilot program called Benefits Delivery at Discharge (self-explanatory), which is only in certain areas. Ask you local military hospital if they have that program.
After you submit the claim the VA will then examine you for everything you put in a claim for (I was examined by a contract docs). After the exams they come back with a determination of disability, which you can appeal if you want.
That is about it. If anyone wants more details then please ask.
