Cancer is a disease of malfunctioning cell division, which has been around since at least the dawn of civilization, is a common human problem: you cannot drive your chances of getting it down to 0%. That said, there are a number of things you can do to lower your chances drastically while also improving your general health.
1. Avoid any type of smoke
Smoke, whether from a cigarette or a barbeque, contains reactive carbon (including carbon monoxide, which is carbon that failed to oxidize completely), and other molecules which are being turned into smoke by the heat. Cigarettes and hookah are worse than breathing in the smoke from a campfire, as these tobacco products regularly contain heavy metals and other toxic chemicals.
Thus there are multiple dangers from smoke: physically drying out the mucus membranes of your throat and lungs; preventing repair and cleaning. Tobacco and charcoal also contain other toxins in addition to the general dangers found in breathing in smoke. Avoid both passive and active forms of smoking to reduce your contact with arsenic, benzene, berylium, and other highly carcinogenic molecules.
2. Stop eating high calorie, low nutrient foods
Cancer cells, just like all cells, require energy to grow. High calorie diets are connected to an increased incidence of cancer. Consuming varied nutrients from natural sources (which have far more chemical “ingredients” than processed foods, but tend to hold fewer calories) makes sure you are giving both yourself and your symbiotic gut bacteria the right stuff. Feeding yourself right will seriously reduce your chances of getting cancer, as well as a vast pallet of other illnesses (as most diseases are a mix of genetics, environmental factors, and diet).
3. Stop heating your food to above 200 degrees Celsius; especially meats
The propensity of fats to react with carbon (which, by the way, is the backbone of literally everything you eat) and form carcinogenic compounds increases drastically at 200 degrees Celsius. Not to mention that by heating your food to this temperature, you are effectively destroy vitamins A, C, thiamine, and folate, making them inaccessible to your body.
Although meat tends to taste very good due to its high fat content, salt, and umami flavor, its industrial preparation exposes it to varying chemicals depending on local health standards. When meat is heated to beyond 200 degrees over charcoal, it creates 2 different types of carcinogenic compounds which together raise your chances of pancreatic cancer by 60%.
Plant based foods contain a wide range of different nutrients and micronutrients, as well as providing fiber that helps clean your intestines and reduce gastric cancers. The level of processing that a plant or vegetable undergoes before your consumption is far less than that path almost all meat-based products take before they wind up in your kitchen.
Growing and eating your own fruits, tubers, and vegetables using aquaponics or an underground greenhouse (to avoid contaminated topsoil) is honestly the safest bet for avoid carcinogens and reducing your chances of getting any type of cancer.
5. Avoid areas with levels of ionizing high radiation, and flying in airplanes.
The fact is that thousands of nuclear weapons were tested above ground within the last 50 years, and that in many instances this has had an effect on the groundwater and land (like in Nevada). Understanding local history and environmental regulations, especially in regard to the water, is a great idea.
Whether you knew it or not, you are also exposed to more ionizing radiation during a plane flight than on the ground. This is more a problem for flight crews than normal people.
Of course, there are a lot of other things you can do to reduce your odds of cancer, but most of those tips are related to specific cancers or not tied into empirical research. I would have added a 6th tip of avoiding contact with plastic (which degrades slowly into endocrine disrupting chemicals; also called xenohormones), but unfortunately we are ubiquitously exposed to plastics all over the world and our ability to avoid them is limited.
Still, if you want to do as much as you can, taking these tips while also avoiding plastics (and plastic water bottles) would be good advice.