I heard this one many times: "I think someone put a curse on me, and now all I've been having is bad luck. What can I do to remove the curse?"
First of all, no Wiccans that I know personally would ever put a curse on someone. Second, it would take a lot to actually put a working curse on a person without it backfiring and coming back to yourself. There are, however, people out there who can, and will throw curses around like their nothing serious. The chances of being the subject of a curse, are slim, but if one should happen to be cast on you, you can clear it up very easily. What I'm about to tell you can also be used if you don't think you've been cursed, but just seem to be having a streak of bad luck/health/etc.
Basically, whatever the cause, you have an abundance of negative energy in and about your body, and you want to get rid of it. First, draw yourself a bath (I like to make it hot, but just be sure you will be comfortable). Burn any type of incense that you like, and keep the lights turned off. You should use candles as illumination if necessary. You should, however, have at least one candle (black or white) burning somewhere where you can easily see it.
Get into the bath, and just relax your body for a while. When you feel fully relaxed, close your eyes, and visualize the negative energy as a black, sticky film covering your body. If the water is hot, picture it evaporating some of the film into the air. When it leaves your body, it heads towards the candle, where it is burned away. If the water is not hot, or if all of the film does not leave your body, "wash" it off. Physically wash your body, and picture the film coming off in the water. When you are done, stay and watch the water, and the bad luck, go down the drain, into the earth.
Another good thing to do after this, is to take a short shower right after the bath. While the water is pouring down on you, imagine that you are showering in a white light (this is positive energy), and see it filling your body.
If done correctly, you should notice a change pretty soon. Sometimes, you may have to repeat the process a few times, but it has always worked for me.