Start by performing five full-range reps followed immediately by a five-second iso-hold in the bottom position with your upper arm approximately parallel to the floor. From there, go straight into four more reps followed by a four-second iso-hold. Then three, then two, and one. After the last rep, lower down as slowly as you can.
Once you can complete the countdown from 5-to-1, either add weight or try starting at six reps and working your way down.