Top Tips:

Keep the patties cold/frozen until they hit the grill.  Unlike other meat that will cook up better if brought to room temperature before hitting the grill, you want those patties cold so they stay together and stay as juicy as possible. Put the patties on a tray or platter, covered, in the fridge while the grill heats up. This helps more of the flavour-carrying fat stay in the meat. Alternatively, place an ice cube in the middle of the patty as another way to minimize the patty from drying out.