Classic sauce and meatballs.
I have measurements, but I find that good meatballs are more a matter of feel. You don't want the mixture soft or gooey, because then they will fall apart, and you don't want them too firm, because then they will be rubbery. Use your judgement on whether you need to add more breadcrumbs or liquid, and always add more seasoning accordingly. Likewise with seasoning - if you prefer a spicier meatball, then increase the amounts of seasonings.
If there is a "secret" ingredient in the sauce and/or meatballs, I would have to say it's the fresh parsley. I've made them without parsley and with dried parsley, and they are not as good.