Watch the I to IV Diminished Lines online guitar lesson by Robben Ford from Solo Revolution: Diminished Lines
It's always fun to play an up-tempo swingin' shuffle, and it's so close to jazz in feel that you can pull ideas from a jazz context into the blues. It's important the way a song feels to know whether or not you want to play jazzy licks. It doesn't work in every context, and the music should be tailored to it, or vice versa.
Keep this in mind while we go through some diminished lines you can play when going from the I chord to the IV chord in a blues.