I have made about 10,000 meatballs in my lifetime. I was making them as a kid, too small to reach the stove.. had to stand on a chair.
Here's my recipe that never fails:
1 pound ground beef or ground turkey
2 eggs
1/4 cup whole milk
Italian flavored bread crumbs
Beat the eggs with the milk until well mixed. Add in the crumbs until the mixture is still pretty moist - too moist to form into a ball, but not wet enough to pour out of the bowl.
(If you goof up and make it too dry, just add some water.)
Add the meat in by hand. Use gloves if you feel weird about using your hands, but you do not want to overwork the mixture.
Form into balls and brown on all sides. (I don't add oil when I use beef, it's oily enough. If I'm making turkey meatballs I might add a little oil to the browning pan.)
Drop the meatballs into the sauce and simmer for at least 30 minutes.