To perform a decline pushup, lie down in prone position. Place the palms of your hands on the surface at shoulder width and straighten your arms at the elbows. Place your feet on an alevated object (bench, table, chair etc.) The rest of your body should be perfectly straight. Only the palms of your hands and your toes should be touching the surface. To begin the exercise, start bending your arms at the elbows and lowering your body down until your chest touches the surface. Now from this position, push with your hands and start straightening your arms at elbows until you are back at the starting position. The higher the object is elevated, the harder the exercise. Remember to keep your whole body straight and to go as low as you can while performing the exercise. Also, try to do the exercise slowly and with control. Pushups train mainly your pectoral muscles (chest), triceps and anterior and lateral deltoid (front nad middle part of the shoulders).