Here's mine, but I won't put in any ratios. These are always tender and very good!
Ground chuck
salt, pepper, red pepper flakes, sweet basil, minced garlic
chopped onion & celery
fresh chopped flat-leaf parsley
1 egg
parmesan cheese
sprinkle of bread crumbs -- Italian or Panko -- (if you use too much, the meatballs get tough)
heavy cream (which helps to hold together & mellows everything out)
Don't overmix. And don't brown beforehand.
These are the "secrets."