It depends one what type you are doing. There several different types. I will address as many as time allows. Regular push-ups build definition. Elevated push-ups do the most work for your chest (feet on the ground and right hand on one chair and left on another with a gap between the two chairs allowing your chest to drop below your hands). This type builds mass and definition. Then there are another kind of elevated push-ups where your feet are elevated on a couch or something but your hands are on the ground. This will even out the tone in your chest. I recommend using all three. There are also diamond, and clapper push-ups. These are an advanced type that, when mastered, will give better results faster. The diamond push-up is where you form a diamond or triangle with your hands (meaning both hands will be directly under your chest) and do push-ups from this position. It is very hard but worth the effort. Clappers (most people are familiar with) are just like regular push-ups, but instead of coming up slowly, you must propel yourself upwards into the air a little bit, clap, and then land back on your hands. Using all the mentioned forms will increase your upper body strength, but I advise using weights in addition to this for more visible results.