In order to truly be a fit force of nature, you need to hit each of these groups. Need some clarification? Here is a simple run-down of what to do to target each one.
1. Cardiovascular Endurace: long distance running/biking/swimming, any cardio machine for an extended period of time
2. Muscular Strength: heavy weights, few repetitions. You know when you see those giants in the gym lifting weights bigger than your house for one rep? They are working on their muscular strength.
3. Muscular Endurance: light weights, lots of reps. This is what will give you long, lean muscles.
4. Flexibility. Simple enough! Stretch!
5. Body Comp. Alright, this isn't really something that you can work on, but just be aware of your fat to muscle ratio. Make sure you've got enough of each! (Yes, you need fat. If I really need to tell you this, please move out from the rock you've been living under.)