I'm a big fan of the close grip bench. I've found it to be one of those exercises that is a great modification for clients who experience shoulder discomfort in it's wider gripped cousin, the bench press. It's also just a great exercise for improving upper body strength.
One thing I've found is my clients are not quite sure about is where to position their grip. I've seen people think that it has to be as narrow as the distance of touching your two thumbs while gripping or both hands have to be inside the knurling (rough part of the bar) on the smooth part of the bar. Not true.
As Eric Cressy explains in the video above, the grip is based on the individual. Those with broader shoulders will be more comfortable with a distance between the hands of 12-14 inches.
A good place to start is placing your index finger where the knurling meets the smooth part of the bar and go from there. Find the grip where you're able to keep your wrists in a neutral position keeping the elbows under the bar.
Watch the video above for full instruction on who to properly execute the entire movement.