During early highschool freshmen-sophomore when I was in shape I used to lift weights on odd days and cardio on even days.
Cardio - Id do 40 mins on the elliptical (about 3.5 miles), then 15 or so min bike. Then sauna for like 15 mins. And stretch.
Weights - Id bike 15 mins for a warmup, then free weights for 45 mins. The lbs of weights were lighter because I didnt want huge man muscles. So i did 12 reps of as heavy as I could do minus 5 lbs. Sauna, stretch.

I was fit in early highschool (3years ago).

Hope that helped? Im trying to get back into it myself.

Hmmm...well I am not in shape but I do have a personal trainer. She has me do circuit training and cardio. On other days we may just take an hour long agressive walk. Any kind of excercise is good. I like Callie's advice. Depends on how many days a week you want to work out. Another worthy investment may be a heart rate monitor. That way you know when doing cardio that you're in the correct range. With weight training...just listen to your body. It's good to be sore the next day but not to the point where you can't move. Just take it easy at first. If you do too much, you could burn yourself out. Maybe keep a little journal to help you understand what works best for you. Good luck!!