I have always had a fast metabolism, so I've never had to work out in my life. I'm not fat, I just really want to tone up my stomach and don't really know how to go about it. Any useful tips would be much appreciated.
Planks work great (elbow, full, side, hop outs). Vups are tough but extremly effective for sculpting your abs. Reverse crunches, leg lifts (figure 8s), bicycle crunches, and burpees work well too. Checkout ab-workouts-guide.com its full of exercises that'll tone your abs and your core (abs, hips, lower back, butt too).
HIIT (High Intensity Interval Training) is extremely effective for burning fat and building muscle. The workouts force you to work hard in short bursts making them a form of cardio exercise.
Good luck and God Bless!