How in shape are you? It's usually best to start out easy. Set aside between 20 to thirty minutes at least three of four days a week. Alternate between walking and jogging. Don't push yourself too hard to begin with, just ramp it up gradually. Each day do less walking and more jogging. In very little time you'll be running the entire twenty minutes.

I try to run around 40-45 minutes a day, time allowing. I feel awful if I don't.