You need fat for a good hamburger.
Most people go with meat that's simply too lean.
Ground sirloin with regular hamburger mixed in, 2/3 to 1/3 ratio, works well.
You also want a coarse grind, and DON'T compress the meat together into a wad. Gently pat it together.
If I'm being purist, the only thing I put on my burgers before cooking its a little salt and pepper.
If I'm being a little adventurous, I sprinkle them with Old Bay.
If I'm out of my mind, I'll add chopped onion and garlic, bread crumbs, an egg, salt, pepper, cumin, oregano, basil, parsley, Worcestshire or Squid brand fish sauce, etc.
Grill over charcoal with a chunk of hickory added.