I consider myself pretty good at hamburgers. The key is medium high heat and dry no oil on cast iron skillet or flat top. Watch the edge of the burger and when it releases from surface you can flip it. It should have a pretty dark crust. Repeat on second side. Last 30 seconds or so place cheese on top and cover until melted. Anytime you press or work the meat too much it gets dry and hard. I like my burgers medium rare to rare so under cooked is I also never salt meat prior too cooking.