In order of most important to least (still important, but not the most important)...

Most Important

1. stop smoking -->plenty of studies show that smoking IS the leading cause of cancer (any google search on the topic should make that clear)
2. limit added sugar, including high fructose corn syrup (ref, Brain Maker by Dr. Perlmutter http://amzn.to/2l41duf) --almost as bad as smoking, next to smoking it causes the most amount of illnesses
3. cut processed carbs such as bread and pasta, or go fully gluten free (ref, Brain Maker) --similar to sugar
4. eat the rainbow in terms of fruits and veggies of all colors in order to get the highest quality/quantity of nutrients --fortify your body with nutrients that heal and protect
5. not always, but more often than not, prefer meats such as fish and eggs over beef and pork
6. prefer no dairy, not all the time, but more often than not
7. incorporate supplments such as vit D (5,000iu), magnesium citrate (400mg), resveratrol (100mg), probiotics (http://amzn.to/2iTLCcz)
8. switch alcohol choices to just red wine more often than not for the resveratrol content --increases positive epigenetic expression (in my own ebook, Forever 29)
9. fast 24 hours each week --also for the positive epigenetic expression (in my own ebook, Forever 29 http://www.forever29nutrition.com/)

"Ultimately, it's not about counting calories, it's about eating calories that count." --Tim

I recommend to implement one of these at a time from top to bottom. But don't go to the next one until you're able to master it consistently for 3 months or so.

No need in triggering the amygdala's natural fight, flight, or freeze response by freaking it out when trying to do too much too quickly. That's probably one of the top reasons people don't succeed. Tip toe around the amygdala with small wins over time.

Good Luck!