I got one of those emails today, from a student who had a rough start last semester and failed my class. The student wants to know how to do better next time around. I don't remember the particulars of this student's difficulties, but there are a couple basic problems a lot of first year students encounter. The good news is that a lot of these problems can be changed for the better.
The other good news is that most professors don't think a student who messes up the first term is a loser or stupid, or whatever. Most of us messed up at some point, and the rest of us have friends who messed up at times.
Here's my short list for doing better in college.
Go to class. I know it's hard to get up early, but being there is one key to doing well. Go prepared, take notes, review your notes after.
Do the homework. Even if it's not required or turned in, do the readings, work problem sets, whatever. This is especially important for language, math, and other classes where you build skills as you go. If there's language lab or a math lab, do your homework there, especially if you can get help easily.
Get help early and often. Your college or university almost certainly has tutoring available. Use it. Talk to your professors about your questions early. Most professors don't bite and aren't evil. Some of us are better explainers than others, but most of us will try.
Study in groups. Get connected with your classmates. Study with them, get to know them. Exchange phone and email information so that you can get notes if you miss class (or give your classmates help if they miss, too). One of the best tests of your knowledge is explaining things to someone else. Studying in groups helps you learn to explain, and so helps you learn.
Do the work. Read your assignments carefully and do them with attention and care. Small assignments add up to a lot over a semester, so take them seriously. Give yourself time to do your assignments well.
Those are my top five; what are yours?