The bench press is another upper-body exercise, but this one requires more work from the muscles in your chest. In this variation, you’ll perform it with two dumbbells (rather than a single barbell). This forces your muscles to work a little harder to stabilize the weight you’re lifting.
Here are the steps:
1. Lie flat on your back. Use a weight bench if you have one, or lie flat on a floor mat if you don’t. If you’re on the floor, bend your knees and place your feet flat, as if you’re about to perform a traditional sit-up. If you’re on a weight bench, bend your knees over the edge of the bench and place your feet flat on the floor.
2. Begin by holding the weights close to your chest. Breathe out as you push them up, continuing until your arms are almost completely straight. The weights will be close together, but shouldn’t touch.
3. Breathe in as you slowly lower the weights out to your sides. Continue until your elbows are even with your shoulders, but no farther. If you’re on a weight bench and you let your elbows drop below your body, you’ll put unnecessary strain on your shoulder.
One of the nice things about the bench press is that it’s only one of several exercises you can do while lying on your back. For example, you can follow up with a pullover, where you lower a weight behind your head (see http://exercise.about.com/od/exerciseworkouts/ss/backexercises.htm for instructions).
Source of Information : Oreilly - Your Body Missing Manual