Split the plate with veggies and meats. Try to include grains, and don't forget your dairy
Just because you wouldn't eat it as a child doesn't mean you wont like it now. Experiment and no you don't have to clean your plate.
Lean proteins will help. Add seafood when you can and gravy is not a food group.
It's ok to have desert so try naturally sweet things like fruit and parfaits with yogurt. Baked apples and cinnamon or a fresh fruit pie could last all week.