This really depends on the kind of cancer that we are talking about.
Of course, smoking is a huge factor in the development of lung cancer, so stopping smoking reduces the risk and smoking increases it.
Chewing tobacco increases the risk of cancers of the mouth and throat.
Being exposed to ultraviolet definitely increases the risk of skin cancer.
Having sex with a carrier is the only way for a woman to get cervical cancer.
Having a good diet can decrease the risk of cancer. Drinking alcohol can increase cancer risk. Eating and drinking lots of things that have antioxidants in them can reduce the risk.
You can follow the links below for more on cancer risks and prevention.