Throughout the history of jazz, the best piano players have always sounded completely fresh while at the same time staying rooted in the jazz tradition. Just listen to any great jazz pianist and you can hear it in their playing.
Keith Jarrett can play can stretch the time as much as he likes while playing a jazz ballad, but you'll often hear him playing steady quarter note chords with his left hand, especially if there's no drummer. This harks back to the early days of jazz when the steady beat was emphasized.
Herbie Hancock can play as far "out" as he likes, but he always knows where he is in relation to the song's form. In fact, he's said that it's not that difficult to go outside the chord changes. It's getting back in that's the challenge!
I've made a video to show you a great way to improvise on the blues. This concept, in which you improvise around a new motif, or riff, in each 12-bar chorus, harks back to the very early days of jazz and the blues. Blues singers in particular would make up a new lyric each chorus, using an AAB rhyme scheme. They's tell a story like this, which unfolded with each new improvised chorus.
We pianists can do this too. Watch the video and give it a try. It's a great way to stay creative and also to give your blues solos a cohesive, naturally-flowing structure.
Here's the video. Good luck!
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