With a knife, score one side (maybe both) of the burger with a tic-tac-toe pattern. This will keep the burger from getting thicker in the center.
Put on a hot grill at a high heat.
Cook about 8 minutes for med-rare, or 10-12 for medium. Flip halfway through.
Don't press the burger! You want to keep those juices in.
The "hand trick" to test for doneness works with burgers, too. Press the burger with your finger and compare it to the firmness of part of your hand. The meaty area at the base of your thumb is what medium-rare feels like. The area in the center of your palm is what medium feels like.
I often don't have tomato juice, so once I used the juice from a can of Rotel tomatoes, and was happy with the result, especially as far as moistening the meat. I wonder how a good beer might work.
The first time I made it, I didn't use salt, so I'm experimenting now with what amount of salt would be right.