Start with 1single push up and when you do it stand up like for a jumping jack and then do another 2 push ups and so on. When you reach the top of the pyramid (10 pushups) take a 30-60 seconds break and start going down the pyramid.
You can apply that schema to any exercise you want like chin ups or pull ups and you can ''play'' with the numbers so for ex. if you are, let's say, on an intermediate fitness level then you can start your routine with 5 push ups and see where this goes. Have fun!