Don’t overwork it. You really don’t even need to add salt and pepper to the meat; all the action is in the toppings. Also, let the patties rest before cooking. Otherwise they’ll be chewy.
Start with a clean cooking grate. Dirt makes food taste bad and makes it stick.
Cook it hot. Heat the grill to between 450° and 550°. Cold burgers on a cold grill are going to stick every time.
Create a nonstick cooking surface. When the cooking grate is hot, wipe it quickly and carefully with an oiled square of several folded paper towels.