What would be the best way to get my skinny legs thicker and a flatter tummy?

Weight training: For your muscle development in the legs - see a personal trainer. If diet and abdominal exercises don't work for the tummy, you might consider seeing a plastic surgeon to discuss coolsculpting, liposuction or tummy tuck.

Body changes: For flatter abdomen eat healthy & get physically active. Calories burned > calories consumed. To tighten ab's: crunches, reverse crunches, exercise ball crunches, pelvic thrusts, lying leg raises, side bridge & “bicycling” exercise on back. Engage in regular aerobic exercise (i.e. running, swimming, Nordic track, bicycling, kickboxing, walking, cross country skiing, hiking, etc.)