Squats, squats, squats. Try doing about 60 bodyweight squats and see what happens..
One legged squats if normal squats are too easy. Good luck. Try to stand up from your chair right now using only one leg. If you can, repeat that with 3 sets of 8 reps =)
Pushups are crucial --> there are dozens of variations (tricep, chest, fingertip)
Sprints, jumprope. Nothing wrong with those..
Handstands.. and after you can hold a handstand for a minte, try doing handstand pushups.
Handstands are killer on your abs and core, holding one for a minute is like doing a hundred crunches... and way more fun in my opinion.
Squats wil tone the crap out of your ass, which is a good thing for most anyone.
You can buy a ab wheel for like $7 that I promise will absolutly pulverize any gut or lovehandles that you might have, and bad backs by gradually building up your core back muscles -->
Amazon.com: Ironman Double Ab Wheel: Sports & Outdoors
meh, that should be a good start. Hope this helps,