Pre-basic: work on PT score. Know what you have to meet and make the numbers. Push for 90%+ BEFORE basic.
During basic: Keep your mouth shut, don't volunteer, don't stand out. Be the gray guy.
As an old ex Drill Sergeant, the whole "don't volunteer for anything" line usually meant you're guaranteed of being voluntold. My advice is keep your mouth shut if you don't have anything constructive to say and be observant. They will ensure you hear how not to do things, but absolutely ask questions if you are unsure of anything, they want you to succeed. Volunteer for everything, even crappy duties can turn out to be learning experiences or even surprisingly fun or rewarding. It is almost all mental, even the physical parts. They will get you into shape one way or another, but being in decent shape before you get there cuts down on the sore muscles and getting used to using them if you're not a very active person now.
You will have a graduation day, even if you get recycled you will have a graduation day, so it will end; try to remember that on those really rough days and nights when you are feeling down, tired, cold, P'ed Off, or just wanting to go home. Be a man of your word to your fellow recruits. Take initiative, don't sit around waiting to be told to do something if you see work that needs to be done or someone who needs help, it will be noticed. Don't let your buddies down, and most of them won't let you down.
Good luck and thanks for deciding to serve.
