A terrific little booklet is "Robins' Laws of Good Gamemastering" by
RPG author Robin Laws. Published by Steve Jackson Games, it covers the
different types of RP gamers, and how to match up your rules and game
with your players. Looks like it's out of print in hardcopy but
available in electronic format: http://www.sjgames.com/robinslaws/
I'm looking forward to getting my copy of Xtreme Dungeon Mastering by
Tracy & Curtis Hickman (illustrated by Howard Tayler of Schlock
Mercenary fame) any day now. Looks like it covers much of the same
material from a slightly different angle and a generous infusion of
humor. http://www.xtremedungeonmastery.com/
Cheers,
John