I am returning to school for Physics after essentially failing at University for Engineering almost 10 years ago. I did well in high school, got into a decent school, and ultimatly failed because my study habits sucked (and my lack of maturity at that time caused me to not realize that). Now, I am doing very well (first semester back will be a 3.5 as my lowest grade) by doing a few things:
1) Find a routine. Stick to it. I work nights in an IT job that allows me several hours of homework time in between processes. For this one semester, I have probably spent more time doing homework than I did for my first two years of initial University - and it's paying off. Having a consistent time to do homework every day can mean lots to your success.
2) Get a support mechanism - for me right now, it's a combination of my wife and a few classmates. In my Calc3 class (of 8 people, started with ~15) nearly everyone comes to class an hour early and discusses homework (the room happens to be open before). With only one exception the class is doing very well as a whole and our instructor has recognized that.
3) Remove distractions. In high school I was used to working on what little homework I did while watching TV, listening to music, on IM, etc. I cannot do that any more (this was part of my initial failure). I can do some things with light music on still, but I do turn it off more than not now. (doing homework in a work environment has made this an automatic for me, but some nights when I do work at home as well I have to clear my desk and center myself)
4) Make school work your priority. This may seem a little redundant - but that means maybe missing your favorite sports team play on the weekends or not being the first to beat a new video game. Learn to reward yourself after working on school work will make this easier.
5) Find a routine! I list this twice, because I mean with your life as well as your homework. Getting consistent good food and sleep can be huge in your overall health and state of mind.
6) Get invested with your instructors. My first time through I distanced myself from instructors and professors because I was very intimidated. I'm learning now that relationships are a key part of the university experience, you're not just a number, but an asset to your instructor and the school. As I've gotten to know my instructors and Professors (esspecially degree-related) it has made them incredibly more approachable. I won't neccessarilly be inviting them to my super bowl party, but there's something nice about seeing them in the hall and being able to say 'hi'.
7) Get involved. This is the part where I haven't hit the nail yet, just getting back into things, but the most common advice that I get about
going back to school is to get involved. Join your local degree-related society, get involved in a project with a professor, go to those random symposiums. These are all things you'll need to do 'in the real world' so if they honestly don't interest you now, why will they in the future?