Find high traffic areas and choke points associated with said traffic. Place a mental marker of head level, could be a box or a line on the wall (go on Pantheon and place your cross hair right above the line on the opposite wall on waterfall side and you will see what I mean). Drag scoping does wonders. You will start to get a feel for where the head is gonna be and eventually be able to run and gun on maps where the ground isn't so level.