My friend R just asked me this question. I buy 90% lean grass-fed ground beef, and mix in a few shakes of ground pepper, and 1/2 tsp per pound of meat of Frontier organic adobo seasoning (ingredients are sea salt, organic garlic, organic onion, organic black pepper, organic oregano, organic bay, organic turmeric – note the wonderful lack of preservatives and anti-caking agents!). They sell this spice at Whole Foods, or you can order it from Amazon (link). I also use this spice in my chocolate pork rub.
After I mix in in very well, I form the patties (a little thinner in the middle, so they’ll cook through better) and then place them on a rack on a cookie sheet in my refrigerator (uncovered) for a few hours (up to a day) until I’m ready to cook them. Being in the refrigerator will “dry-age” them, reducing moisture and concentrating the flavor of the meat. Plus, it saves you time when you’re actually cooking.