There are not really any lifestyle interventions with good quality evidence for preventing cancer. This is my list:

Definitely worth doing:

- Don't smoke anything that burns or chew tobacco.

- Depending on your age and sexual experience, get the HPV vaccine.

- Investigate your family history of cancer. If there are multiple people on one side of the family getting cancer (particularly breast + ovarian + pancreatic, or colon + gastric) then consider getting genetic testing/discuss with a doctor.

- If you have certain ethnicity, just get a genetic test, pay for it if you have to (Mainly for Ashkenazim)

- Avoid consuming herbs/plants which contain aristocholic acid.

Probably worth doing:

- Reduce red meat consumption (observational data and plausible mechanism)

- Reduce or eliminate alcohol (observational data and plausible mechanism)

- Eat highly processed meats rarely (charcuterie etc)

- Make sure to get sufficient fruit and vegetables and fibre. This may offset the risk of red meat consumption.

- Take vitamin D, particularly if your levels are low or you live far from the equator. Don't take intermittent megadoses, take some every day. This seems less useful if you are overweight.

- If you are female, then have children and breast feed if possible. Longer durations of breastfeeding are more effective. Having more children is also more effective. (One may balk at this, but there is a lot of supportive data about long term breast cancer risk)

- Exercise. There is only (a ton of) observational data, but exercise is so universally beneficial. Going from nothing to a bit of exercise has a bigger impact than going from a bit of exercise to a lot. Most people over do it. Do cardio and resistance training. Try to do something every day.

- Avoid supplements designed to have antioxidant properties (based on data suggesting harm from controlled trials, and no clear benefits).

Maybe:

- Move closer to the equator.

- Avoid obesity (note this is complicated... obesity itself may not be the problem. Obesity is protective for some cancers, and this varies by age).

- Get checked for Hepatitis B and C, particularly if you have risk factors or were born/grew up in an endemic country.

- If you get chronic reflux or heartburn, consider pushing for your doctor to investigate further (usually a gastroscope) and do an H pylori test. This is particularly if you were born/grew up somewhere with a higher chance of exposure. If you have it, take the eradication therapy.

- Try to maintain metabolic health. This is highly personal and hard to give general advice around. Eg. South east asian/Subcontinental people can be metabolically ill despite not being overweight. Investigations here could vary from checking for insulin resistance (eg HOMA-IR calculation from a blood test), gettinga DEXA scan to look for visceral fat, or in the extreme case continuous glucose monitoring to look for foods which really spike your blood glucose. The interventions are exercise, sleeping well, and potentially avoiding foods which spike your sugar (or scheduling exercise after eating such foods). Soon we will have a better idea if certain personalised dietary interventions may be beneficial.