Oh the figure 4! How I love this sucker. (Little known fact: just about anywhere else in the world it is called 'The Yaniro')
My 2-cents on this move. The steeper the wall the better, though I have the most success with this at 30-45 deg overhang.
The fig-4 hold should be a single hand, directional, monster jug that is very difficult to match. e-Grips 'jibber jabber', not the ring one, is ideal. Place it at a slight undercling angle to prevent matching.
They need to come into the fig-4 jug from the side, not from below. The hold they are coming from needs to be so directional and/or duo-tex so it cannot be used as a foot. Do not allow any other potential foot options once they hit the fig-4 jug
The 'target hold' they are going to needs to also be single hand and directional, but not a jug. It needs to have enough bite to allow the climber to unwind the fig-4, but small enough and directional enough to prevent campusing or matching. (Bear in mind that Sharma-like talents will just campus anyways, but we usually aren't setting for those cats!)
Most important: The target hold also needs to be located above and off to the side of the fig-4 jug, about the distance of a big cross thru, approx. 3' over and 1+' up.
The next move needs to be far enough away that having the correct hand on the target hold is critical.
Expect most climbers to hate your problem until they figure it out or are shown the correct beta! It is cool to see done well, but most have no clue how to execute a good fig-4, even if they understand the concept: pinch your wrist with the knee, not your elbow!!!!!
Have fun!