If you're having trouble establishing a mind-muscle connection with your triceps then begin the workout with something that puts the muscle into a shortened position, and work isometrics (holding the contraction) to help with that. Try a pushdown variation. My favorite for this is the reverse-grip pushdown.
Make a concerted effort to roll your knuckles back towards your body and hold that for a 2-3 count for 3-4 sets.
Fifteen more workout tips from Bret Contreras, including assisted one-arm push ups, the merits of heavy back extensions, the benefits of the "clam raise," and more.