This is an excellent book and commonly used in aeronautical engineering undergraduate courses.
Also, there is much to be learned from helping maintain the aeroplanes you are flying - talk perhaps to private owners, or if you join a syndicate see what you can do to muck in. Even doing the regular cleaning, it's amazing how much you learn.
POHs are generally pretty simplistic documents, but quality time crawling around the aeroplane (pick a rainy day when nobody else wants to fly) with the POH is always worthwhile.
G