In bar 4 of a 12 Bar Blues, you can nearly always add in a climb up to the IV chord - for both a standard form and a quick change.

If the band are listening then it's likely that some of them will 'pick it up' and join you for it - but it works if you do it on your own too - and it's great if you playing solo too.

There are a bunch of options, you can play single lines, power chords and also as chords!

Start by moving up a tone from the I chord on beat 2 or bar 4 and then step up chromatically (1 semitone at a time!) and you'll get to the IV chord on beat 1 of Bar 5!