It's going to depend on what kind of results you're looking for. If you're just looking to burn off some fat more easily, then a daily cardio routine is just about all you need. Find an exercise that you can do intensely enough to get your heart rate going, and do that for 30-40 minutes a day. I personally enjoy mountain biking.
If you're looking to tone your muscles a bit, you can integrate a body weight strength training routine three days a week. Simple exercises such as squats, push-ups, pull-ups, and sit-ups can be enough to keep your muscles feeling firm and toned.