Undoubtedly the most unpopular exercise in existence, the push-up is a fabulous conditioning movement which has been abused in purpose (punishment) and execution (those who hate them invariably can’t do them correctly). But this simple movement not only targets the chest, shoulders and triceps (the “pushing muscles”) but develops the same core stability as the Plank exercise (the static pushup position, sometimes done on the forearms). These require no equipment, and can be done anywhere, anytime, by anyone with arms, and virtually anyone who practices them faithfully can progress to the ability to perform dozens -which any serious athlete should be able to do. Keep the body straight, lead with the chest, go to down to at least parallel.
Once you can do twenty or more, do them with your feet elevated, hands on (hexagonal) dumbbells, with a loaded backpack, or with one hand on a medicine ball.