Start by a little bit every day, spend 5 minutes when you wake up and 5 minutes before you go to bed to do some form of asana, be it stretching in a couple of poses, or a couple of sun sals. You will come to enjoy it and those 5 minutes will easily become 10 or 15 minutes.

It's all about stepping on the mat, or whichever survace you use to practice on.