Agree with everything said here thusfar, and I just thought I'd add to it and expand upon some.
Bust your ass in TBS, it actually does matter. I finished TBS number 24 in my class, so I got promoted to Captain before all my peers (six months ahead of some of them).
Wear your goggles during night land nav, no matter how much you get laughed at. I stabbed myself in the eye with a tree branch, and was terrified for a good solid month.
Remember, the fleet is an evil mistress. Enjoy your time off when you have it, because you aren't going to get it back, and the Marine Corps can find ways to fill your time for you. Specifically in relation to flight school. In your off time, don't worry about studying - unless it's chicks and beer.
Finally, when you're no longer having fun - it's time to get out.