Play 4-card majors, with just Stayman and Blackwood as conventions, and jumps stronger than non-jumps. Any old books by Goren you can find at a used book store will serve as texts. When your players get a little better, show them Five Weeks to Winning Bridge by Sheinwold. Then let them loose.
Alternatively, Edgar Kaplan's Bridge for Dummies is a good modern introduction to the game by one of the best bridge writers of the 20th century.