I'm just starting
Welcome to Skimble Amy!
The best thing you can do is have a well rounded program. Think full body resistance training, cardio, and eating right. Cardio alone will more than likely strip your muscle mass down. That's not healthy! Working certain muscle groups and neglecting others can lead to muscle imbalances. That's not healthy! Working out, but eating bad can lead to frustration because your not looking or feeling your best. That's not healthy :)
Nutrition actually plays just as big a role in the way you look as your exercise does. Focus on getting natural foods containing the key words water, fiber, and protein.
Good luck & keep us updated!