If I want pronounced grill marks on protein, or anything else for that matter (vegetables, fruit), like keeperofdeflame says, start on a hot, well-oiled grate close to the fire, but with the flames controlled so as no to engulf and burn the surface of the food.
If you want pronounced grill marks in a crosshatch pattern, try using the 10AM/2PM method; start with the presentation side of the food face down to the fire, with the food oriented to 10 AM vis a vis the grill bars. Allow the food to acquire grill marks as deeply colored as you please in this position, but not so black as to be or taste burned, then, without flipping, lift with spatula (delicate items) or tongs and orient to 2 PM vis a vis the grill bars until you've got the coloring that you want. Of course, monitor internal temp as you go--pretty grill marks do not make up for overcooked food.
When satisfied, flip to finish to desired internal temp. Grill marks on the second side are not important-moist, tender, juicy food is. For me grill marks are eye candy; they can add to our overall enjoyment of the food, but are not overly important except aesthetically.