But where do you start?
When it's time to start working on specific body parts, avoid burning yourself out too quickly. Start with big muscle groups and multi-joint exercises. If you wear out the muscles that only work with one joint, you won't have the strength you need to work your bigger muscles. I like to begin with the legs. Your femur is the biggest, heaviest bone in your body, so moving it takes a lot more work than any other part. Keep the heart-rate up; include jumping exercises (if you can) throughout the workout. If you have bad knees, talk to a personal trainer in your gym for modifications.
When you work your arms, stick with the same rule as before: multi-joint exercises first. Pull ups work the shoulder and elbow. Front raises only work the shoulder. If you start with front raises, you'll find yourself doing less pull-ups than you're actually able to do (I know, "less pull-ups" sounds awesome because no one likes them... but your back will look way sexier if you do them!) Similarly, do your push-ups before your pec flies.
Finish with your abs. Why? Because you NEED your abs to assist you with the rest of your workout. You should maintain a tight tummy with every single exercise. (*Don't know how? Imagine someone is about to punch you in the stomach. Did you feel your stomach tighten up? If not, put your hand on your gut and cough.*) If you start with your abs, you'll feel low on fuel for the rest of the workout, maybe even less coordinated.
End the whole thing with a nice stretch from 3-5 minutes. DO NOT SKIP THE STRETCH. Stretch because it feels great, will improve your flexibility and ROM, help prevent knots and finally, because I said so!
Eventually, you'll want to switch it up, maybe work different parts on different days, whatever. This is just a good way to get more work into your workout. If progress is slow, just remember that SLOW progress is STILL PROGRESS. Be patient, be consistent and soon enough you'll reach your goal and beyond!