Myron Mixon has a book out. I haven’t read it yet, but if you have seen him on BBQ Pitmasters or heard of him, he knows what he is doing- as he has made a lot of $$ on BBQ. Johnny Trig might be another one to check on.
Otherwise, I also used the internet and a few sites. People post their rubs, etc on there. I sure learned a lot this way. If you want- you can PM me for the sites I use.
Good luck, if you get into it it is a great hobby and lots of fun.