Face pulls are a staple in powerlifting circles, and they've trickled down to the general lifting population, where they've helped legions of guys fix jacked-up shoulders due to poor programming choices when they first started out.
By serving to help offset all that horizontal and vertical pressing, the face pull can rejuvenate your lifting (or at least pressing) career while conditioning the rear delts, rhomboids, and external rotators. It can even help make your posture decidedly less Neanderthal-like, which is a plus unless you're dating a woman who's into the sloped-head, knuckle-dragging type. (I'm told they're out there.)
Unfortunately, there's a problem. The typical gym rat performs face pulls so poorly it's a miracle they don't injure themselves further.
Face pulls Aren't "Power" Exercises
Use excellent form when doing face pulls. Here's what you should do:
Attach a rope to a pulley station set at about chest level.
Grasp both ends of the rope with a pronated (overhand) grip.
Step back so you're supporting the weight with arms completely outstretched and assume a staggered (one foot forward) stance. Bend the knees slightly for a stable base.
Have a partner (optional) place their fingers along your spine at about the mid-back height. This helps remind you not to use the low back to move the weight.
Retract the scapulae (squeeze your partner's finger with your shoulder blades) and pull the center of the rope slightly up towards the face. A good cue is to think about pulling the ends of the rope apart, not just pulling back.
As you near your face, externally rotate so your knuckles are facing the ceiling.
Hold for one second at the top position and slowly lower.
Notes
Avoid using too much weight with face pulls. Going too heavy forces you to involve the lower back to complete the rep, completely defeating the purpose of the exercise and ratcheting up the potential for injury.
Don't push your head forward to meet the rope. This bastardization looks like you're trying to fellate the Invisible Man. For the sake of the children, please don't do it.
Don't drop the elbows. Keeping the shoulders-elbows-wrists in a straight line keeps the emphasis on the upper back musculature; dropping the elbows into "low row" position involves more lats.
Don't go too fast. I know many big, strong bastards blast through their face pulls explosively, but for most this is a movement best hit with a slower, controlled tempo, especially at first.
If you don't have a partner to keep your back in check, try filming a set to verify your technique. You might be surprised just how ugly your form really is.
According to an article by Hartman and Robertson, an underhand grip may be a better choice than an overhand grip. If nothing else, I suggest playing around with both variations.
Stretch the pec minor between sets. The standard "doorway pec stretch" will suffice.
Wrap Up
There's a reason the monthly muscle rags run arm training and bench press articles every month – this is what the average ham and egger gym guy wants to read, and it's certainly what they want to train.
But you're not a kid anymore, and you're supposed to be wise. And a big part of training wisdom is knowing that what you need is more important than what you want.