Three Things You Can Do to Save Yourself a Lot of Trouble
1. Save often
Just like every high school computer teacher told you: saving whenever you make a decent amount of progress or when you get to a point where you're pleased with your work is an important habit to get into. This way, if you mess up beyond what you can undo, or if Photoshop crashes, you have a recent save to pick up from. This is easily the best tip anyone can give you to help avoid any major Photoshop disasters.
2. If you don't like it, change it.
Don't leave something in a project if you don't like the way it looks. This is the worst thing you can do. Chances are, if you love the project except for that one little (or not so little) bit, you're probably going to dislike the project overall. So fix that tiny bit of misaligned text, that wonky graphic or that oddly drawn hand until you like it. It makes for a better project over all, and one you'll be proud of.
3. Practice, practice, practice.
Photoshop is not magic, and you shouldn't think that as soon as you start working with the program that you will produce stunning pieces of work. Photoshop professionals from all fields have had years of practice, and several have attended classes and workshops to gain an understanding of the program. Look up some of the free tutorials available and try them out, even if they don't seem to fit with anything you're working on. You'd be surprised how easily you can apply the same logic of different tutorials to your projects.