If you’re able to do pushups then BRAVO!! YAY!! WOO HOO!! You rock!!
If you’re not able (or not able to do very many, which likely includes the vast majority of people) then you still rock. But don’t despair – instead, practice!
The absolute only way that you will ever get better at this task, or any endeavor for that matter, is to work at it. You certainly wouldn’t expect to pop off the couch one afternoon and go run a marathon, would you? No, my ambitious friend – you would train and train and then train some more. And so, same theory applies here.
Your first step is to get thee on those hands and knees (mind out of the gutter, people!) and do whatever you can do. Pump out several (as many you can manage), then rest, and then repeat. Do several sets. Be regular. Be persistent! Muscles get stronger only when you repeatedly use them.
If you can’t even manage to do them on your knees, then by all means get even more basic and lean against a counter or the wall.
Be negative, too. Thumb your nose at gravity and, starting at the top of the movement, lower yourself very, very slowly. This will help bolster up your strength so that pushing “up” will eventually get easier.
Work on keeping your shoulders retracted as this will pull the focus from that area to your back – which is where your power for this movement should be coming from. Don't want to stress out your lovely shoulders!
(image uploaded to Flickr, mikebaird, 2/14/07)