Pyramids starting at 21 (66 pushups and the entire process it to be done fast with nobreak.)
21 pushups (regular)
19 crunches
17 diamond pushups
15 crunches
13 pushups (regular)
Repeat to you get to one
(once you master 21 start at 23, and so on ans so on)
I do it anytime
It is really a quick workout that you can do before you get into the shower for example...that is what I do at least. And it is really effective if you start off with the right number and it is a great warm up for training.