I don't know what your health is like, but I'd give myself at least 30 mins of exercise 3 days a week. I'd do 15 minutes of cardio workouts and then 15 minutes of resistance/weight training. When I'm trying to get in shape, these are the activities that I do:
Cardio: running, stairclimbing, jump roping, mountain biking, boxing
Resistance training: pullups, pushups, barbell curls, bench press
You may want to add more weight training exercises to exercise other muscles. It all depends what your goals are. But I highly recommend 15 minutes of cardio and 15 minutes of resistance/weight training. Both of these together are great for decreasing body fat percentage and increasing muscle mass.
Start out slow and give yourself a variety of exercises so you will not become bored. Remember to stretch before doing your exercises.
And your diet: If your overweight, then I'd personally recommend cutting out all breads and sweets. Alot of people would disagree with me on that, but it works for me when I'm overweight. If you must eat bread, eat it early in the day. If your underweight or want to maintain weight, then breads would be ok. Focus your diet mainly on fresh fruits, vegetables, whole grains, and lean meats. I'd stay away from red meats as much as I can. Fish would be the best source of meat. I typically eat fish and chicken. Don't eat the breaded type, but the lean type. It's best to grill or bake it when you can. Try to get in the habit of eating a fresh salad at lunch and dinner. When snaking, eat fresh fruits. Stay away from carbonated drinks. Drink plenty of water (8-10 glasses a day.) Take a multivitaming daily.
It may be hard to adjust to this lifestyle in the beginning, but as time goes on, it becomes fairly easy to live by. I noticed I craved junk food less as I stuck to the diet.
The best website I've found on diet and health is
www.ex-rx.net
Take care and God Bless.