How many muscle groups should I be working on each day?

This really will depend on what type of workout you are performing. There are many different ways on how to design a program. The most simplest would be to perform a total body workout 2-3 days per week. In this workout you will exercise all the major muscle groups of the body. Usually you will perform 1-2 exercises per muscle group. The sets and reps will depend on your specific goals. You should rest 1-2 days in between workouts and it is ok to do the same workout each day. It is a good idea to change up the exercises every month or so. Another popular routine is a split routine. If you have to work out two days in a row then this would be a good idea. Here you can split the body in half. For example you can do all upper body exercises one day and all lower body exercises the next. It is always important that you rest the muscle group worked at least 1-2 days. Personally, I enjoy total body workouts. This way you can work out muscle groups multiple times per week. Also when you work out multiple muscle at once you are more likely to burn more calories. Most importantly make sure you switch it up. Try one month of total body workouts then the next a split workout. Just avoid doing the same workout each time you go.

Mike