A few thoughts that come to mind:
-- Pick the professor, not the class. Ratemyprofessor.com is a great tool for achieving good grades. The wrong professor can make a class on Iowa State Basketball History miserable, and the right professor can make a 400 biology class an easy A or B. I graduated with a very good GPA, and a lot of it was due to one professor who I took maybe 8 or 9 classes with and was guaranteed a minimum of a B+, and that was with next to no effort.
-- I got a long ways treating partying as a reward. If I knew I wanted to start drinking by noon on Friday, I made sure there was a list of things I had to get done before noon on Friday. At least for me, partying was more fun knowing I had that paper or outline done, and it kept me on track when doing it as I had a "light at the end of the tunnel" so to speak.
-- This has been mentioned before, but there is a lot to be said for just acting the part. When you're walking around or when you go somewhere, if nothing else act like you know what you're doing. Confidence goes a long way.