You are wise to start now! It will make your recovery so much easier.
The most important thing you to concentrate on is not injuring yourself. The pool suggestions are really good, but if you don't have access to a pool, walking is great! Get a good pair of quality running shoes (go to a running store and get fitted) and then start walking either outside or on the treadmill. The goal should be to get to a pace where you are breating a bit heavier and breaking a sweat.
Listen to your body! If you feel pain, or have issues breathing, stop. Also, stay hydrated.
Most importantly, HAVE FUN!