What's the best exercise for toning my abs?
One of the best exercises for your core is planking. Hands down. Plank exercises will help you tone up and flatten your stomach, because it works each and every muscle. Start off with a regular plank and try to hold it for 30 seconds. Rest and then repeat twice more. As you become stronger, you can add variety to the exercise (here's a good list), but make sure you use proper form by tightening all of your muscles from head to toe (especially your abs), keep your shoulders aligned with your knees and neck in line with your spine.