Grill marks are fairly easy to create if you follow some simple guidleines
start with a hot grill
place meat on gril
Cook appx half amount of time on "side A" (if total cook time on "side A" is 6 minutes cook for 3)
use tongs and give the meat a 45 degree (quarter) turn, cook for remaining time on "side A"
flip and repeat.
Do Not check or move the meat every few seconds or so, let it cook.
DO NOT MASH DOWN on your meat either!!!
DO NOT USE FORKS to turn the meat USE TONGS! (doesn't poke the meat and let the good juices run out)