Regular exercise on a daily basis is important, but doing exercises correctly is vital. The best way to learn proper posture and movements is to have the guidance of a certified fitness trainer. A knowledge of which muscles are being worked is critical as you visualize those muscles being engaged. It cannot be emphasized enough that you must have your head in the game when working out.
As I am doing these pushups, I am keeping my core abdominal muscles engaged. It is also impotant to breath in as you lower your body and to exhale as you push up. If you hold your breath throughout, pushups can be unnecessarily exhausting. One of the most widely performed exercises, it can be performed in a hotel room with no special equipment. Here I am using an upside down Bosu ball which brings in an element of balancing left and right. If you cannot do a standard pushup, start with your knees on the floor until you build up your upper body strength.