Put a monster mini or mini band around your back and hook it in your thumbs. Grab your dumbells and lay on the bench. Slowly bend your elbows until the DB is on your shoulder. Let the dumbbell roll back a little more from there for an extra stretch. Try to keep the DB in the bottom for a second to get some extra stretch and tension time on the tricep. Punch and squeeze your hands to reverse the dumbells up.
There are a ton of variations of this movement. The big thing is don't do the same one all the time and just get some pressure in your triceps. You've got to load the triceps up, you shouldn't get this in your shoulder. Sets and reps can be anywhere from 3x6 to 6-8 x 15, for time in a superset or light weight for times sets. It all depends on your weakness and priorities.