I have been an instructor since 1989, I worked with over 30 people, washed out about 5 and here is what I will tell you.
attitude, if you go into a facility with a know it all attitude, you had best KNOW IT ALL, including how to separate traffic, because the amount of help you will get will be small. You're an ex-military controller who has controlled airplanes at any base and are going to a center, you really do not have a big advantage. Confidence is good, be cocky is not, if yo don't know the difference, you're already in trouble.
Open Mind, this goes with attitude and to me is the most important, be a sponge, absorb everything you can.
Study, look, listen and learn. The people you are working with have already done what you need to do and many believe the system has gotten easier. So you MUST study and learn the information given to you. When you get to your area, know your map, like you know your phone number, study it all the time. Know the LOA, instructors and others will ask you things all the time and they will expect the right answers.
Give 100%, because if you don't want the job, why should I bust my butt, the 10% extra pay is not always worth the extra stress to me and I already have the job. I have worked with students who where getting ready to wash out and if they put in 100%, I will give them everything I have to help them make it, but they have to want it.
When you get to your area, controllers will joke with you (some times we are weird people) and it is ok to joke back. As time goes by, you will learn who you can joke with and who you can not.
Remember this, not everyone is made to do this job.
Most controllers will tell you this is a great job, we are not always happy with whom we work for, but we love the job. Don't expect a lot of pats on the back, but controllers will tell you if your doing it right.
Good Luck to all of you