I'm going to start with antioxidants. The role of antioxidants in the body for cancer prevention, and the immune system in general, is crucial. There are two main antioxidants that serve major functions in our body, Glutathione and CoQ10. Glutathione eliminates environmental pollutants in our body, and CoQ10 decreases our risk for several cancers. CoQ10 can be taken as a supplement.
Glutathione, on the other hand, is made in the body. The following article shows some ways you can increase levels of Glutathione in your body. I am doing all but #4, N-acetyl-cysteine, because of the negative side effects associated with it. There are other antioxidants that are important as well, such as aged garlic, but this is a good starting place.