Watch the Sweet Down Home online guitar lesson by Jeff McErlain from Blues Guitar Fakebook: Rhythm Vol. 2
Some advice, learn as many song as you possibly can. Nothing is too simple. Memorize the songs. Run over them. Make a list of songs you know. Vary the kind of songs you know. Relearn the songs in different keys (singers may not be able to sing in the key you know the song in). Play with the original recordings. Seek out different versions of the songs.