If you coat meatballs with thickened teriyaki sauce they're really good. I recommend this for people who don't like vinegar (since Japanese meatballs tend to have a vinegary sauce).
I made deep fried meatballs with teriyaki sauce, for my husband who isn't too fond of vinegar.
I don't have any hints, but the onions are tastier if you chop them by hand instead of blitzing them in a food processor. Our standard recipe for teriyaki sauce is Recipe ID: 655656
Enjoy Japanese food around the world.