Almost anything scuba related can help hone your skills. I tend to be a believer in reading and in getting several different points of view on an issue. (I could get into learning theory related to this, but I won't.) There are several titles from Watersport Books and Aquaquest that are quite good and usually deal with specialty areas.
There are are also a few techical diving manuals around that provide a lot of basic information that is missed in the present day OW and AOW classes that were part of the normal OW scuba certification process in the past.
There is a lot of interesting and relevant information in these types of techical diving books - just don't let it be a substitute for advanced techical training or diving experience. The best way to hione your diving skills is to dive, dive often, and dive anywhere you can. If you are only making 10-12 tropical dives per year, you are probably never going to get anywhere close to being truly proficient.
There are also a few books around dealing with diving that are also just plain interesting to read and still are quite efective in terms of vicarious learning. "The Last Dive" by Bernie Chowdhury, "Deep Descent" by Kevin McMurray, and "Neutral Buoyancy" by Tim Ecott come to mind. "Descent into Darkness" by Edward Raymer is also an interesting read even it it does involve hardhat diving.