firstly, you need to start with good quality ground beef...the best I've had is the black angus beef from waitrose...fabulous stuff! I usually use all beef, but it's good to sometimes use about 2/3 beef and 1/3 very good quality ground pork.
Anyways, the beef (and pork if you like!), salt, pepper, a bit of garlic powder and some italian herbs (whatever you like, but they can be left out!), an egg to help bind, finely minced onion and green pepper if you like, then either cooked rice, bread crumbs, or some quick cook oats as a filler. Mix well with your hands, then roll out into balls...I tend to make them about 1/2-3/4 inches, then into a large pot of boiling water: Do not overload the pot! Do a few at a time! They will float well when they're done. Use a slotted spoon to remove and put them into another pot or into your crock pot, then pour over your favorite sauce and let them simmer about 20 minutes on the stove or for the day in the crock pot...perfect for throwing onto spaghetti or making a yummy meatball sandwich topped with grated mozzarella!!!