1. Check your credits. Make sure you're on track for graduation. If not, start making arrangements for night classes or summer school or online classes or correspondence courses.
2. Do a final check for any scholarships or awards for which you might qualify. Even honors without monetary awards look great on an application.
3. Check with your teachers about grades. If your scores aren't where you want them to be, ask your teachers what you need to do. Be sincere. Don't act like you just want to pass the class, but act like you really want to learn the material. After all, that is what you're in school for.
4. If you're a senior, double check everything....grades, credits, scholarships, graduation invitations. Most of the time your counselors are going to guide you through the process, but it doesn't hurt to check everything for yourself. Make sure you're paying attention to everything your counselors tell you.
5. Again, if you're a senior, and you're planning to attend college in the fall, make sure you have everything in order. It's easier to take care of everything now while schools are in session. You don't want to wait until the last minute.