If there is one exercise that is hated by most women and loved by most men it would have to be press ups. You know the drill; get onto the floor, kneel on all fours; wrists under shoulders and knees under (or behind) hips. Now bend your elbows and bring your chest towards the floor. Now push yourself back up. Now do it again, lots of times 
Men like this exercise because their shoulder and chest muscles tend to be quite strong; women hate it for the opposite reason – weakness in arm, shoulder and chest muscles. Working all these muscles at one time is a very efficient way of exercising, but the ensuing discomfort as the muscles tire is unpleasant to say the least, which is why most women would rather jump off the roof than add press ups to their exercise routine!
Everyone should do press ups and should learn to do them properly; however even if done with poor form they will strengthen something! Performed correctly, press ups are an unbelievably effective way of conditioning shoulders, chest, arms, back and core muscles.
There aren’t that many other compound exercise that will do so much good in such a time- efficient way. If you worked all these muscles separately you would have to do pec deck exercises for the chest, shoulder press for the shoulders, bicep curls for the front of the arms, and tricep push-backs for the back of the arms. So by getting down on all fours and performing two sets of press ups you can give yourself a quadruple whammy and be halfway through your exercise routine before you even know it!
Press ups are even more important as you age as it is one of the few exercises that makes you lean on your wrists, thus forcing the bones in your wrists and arms to strengthen. Bones are like muscles in that they are designed to respond to the strains placed upon them – if you lean on your wrists often enough they will grow stronger in order to bear your weight. This is one of the guards against progressive osteoporosis; if your bones are going to thin and become brittle then they will eventually, but working them will make them stronger for longer.
Take a look at the Iron Gym which can help you perform press ups in better form.