I prefer to do pressdowns with a reverse grip, because it feels like so much more tension is placed on the innertricep.  As with normal pressdowns, stand in front of the pulley, gripthe bar with (in this case) an underhanded grip about 10 inches apart.  Keep your elbows stationary and your body steady.  Do not lean forwardor round your shoulders!  Press the bar down as far as possible,locking out at the bottom of the movement.  Squeeze for a count of two,then return to the start position.

Done with Dropsets - A dropset is also called "running the rack".  You take your workout weight and lift until momentary failure, not resting, you grab the next lower weight and lift to momentary failure, then not restingagain, grab the next weight down and lift until failure.  This could goon for several drops, but I usually only do it three times.