If you're unused to exercise check with your doctor before start. Once you get going, build your own strength gradually, gently challenging yourself a day to go a little further, a little faster possibly a little for more time. Straining yourself too much within injuries and when it is too very fast you'll end up giving back up.

You will be hit plateaus and that welcome because tells you it's time to adjust something keep plan your body constantly changing to everything you can do.