Here's my recommendation: Find an exercise that you enjoy and do it. Thirty minutes to an hour per session will do the trick. If you don't weight-train, I recommend checking it out. And when it comes to exercise, don't overdo it. No need to get an injury while you are trying to be healthy.
Here's an exercise tip. When running your errands, find a parking space far from the store. Those extra few minutes of exercise will add up!
Source: Weighty Matters (I'm a big fan of this blog)