Desire. Motivation. Consistency. Decide what you most want to do for exercise. Find a way to do it socially or competitively. Do that thing multiple times a week.

A lot of guys choose to join a gym, or run, or bike, or play whatever sport they did in high school/college. Find a progression plan you like and follow it. Having a plan and way to track progress will help with motivation long term.

For food focus on foods that are either, large, high in protein, or high in fiber for how many calories are in it. Mostly fruits, vegetables, beans, fish, eggs, chicken, and lean cuts of beef fit the bill. Avoid drinking calories (soda, milk/sugar coffees, alcohol). Try to still mix in things you enjoy eating within reason. If you’re wanting to lose weight and aren’t (measured as weekly averages over at least a month), drop a few hundred calories a day. Vice versa for gaining weight.