I dice an onion super fine...almost to mush, but don't be tempted to blend it or it goes watery
decide on a theme if you want fancier burgers....
italian: add a blob of pesto, plenty of oregano, smidge of garlic, form burgers around a blob of mozzarella
smokey: smoked paprika, chipotle chilli
mexican: mush in some kidney beans, add chilliflakes
pork and apple: blob of whole grain mustard and a grated apple
pork and black pudding....either add in chunks or form the burger around a thin slice
the world is your oyster!!
Use PLENTY of S&P and really really squish the meat together, do not bother with any additions like crumbs/flour/egg it really not necessary if you squish the meat firmly
Take a tiny piece and throw that into a hot pan and cook both sides to taste and check for seasoning and once you are happy with that then form the burgers and set them on a board and chill for a couple of hours before you cook them. Make them at least 6 oz, anything less is just stingy and skimpy looking!
Use a very hot pan/griddle and do not be poking them about, like steak in a pan, if it's not moving it's not ready to turn.