Help me get back in shape!!!?

I injured my knee over the Summer AND got Pneumonia within months of each other. Prior to that, I worked out 5-6 days a week and I was also on a Roller Derby team which was 4 nights a week. After getting sick, and the injury, I gained 15 lbs and became lazy and depressed. Now, I am finally ready to take charge of my life again, but do not want to burn myself out. What would be a good work-out regimen that will not be overwhelming, but will give me results? And how long should I do that until I go full force again?