There are diffrent things you can do for diffrent types of Cancers, like for skin cancer use sunblock when you are going to be outside, this cuts down on the UV rays that your skin absorbs. Avoid...
The most effective vitamins used for cancer prevention are:Beta-carotene10,000-25,000 IU, Folic acid selenium, Vitamin C,Vitamin EPlus a multivitamin/mineral supplement
Don't smoke or be around people who smoke, exercise like going for a run at least twice a week and eating right. Do all of these and hopefuly you will be fine.