Paul Kirk,The Barron of BBQ, is a great place to start because he gives some great "DO's and DONT'S" that will help you stay away from some major mistakes. He also gives you some great rub recipes that are tried and tested. Try one and then make some changes to get the rub you want. He also expresses that recipes are just guidelines once you have a good base you can change it up and make your kitchen your laboratory. Some of the guys that are big time competitors now might let it slip that this book helped them get their start.
Big Bob Gibson's BBQ Cookbook is written by Chris Lilly. Lilly and his team have won big, and when I say big I mean multiple championship from the Big 3 (Memphis in May, American Royal, and The Jack). What I really like about his rub section of the book is it helps you start experimenting. He gives you something to try and then shows you how to add on to get the flavor profile you want. In my discovery I found this to be very helpful.
So go to your local Spice specialist (I go to Penzy's Spices) keep experimenting in the laboratory and on the smoker, the quest is to be in search of some Righteous 'Que.