The late Jose Hierro, one of the most prominent spanish poets of the last century, once said that rhythm is the only thing that separates poetry from mere journalism. Being a voracious reader of poetry myself and a keen jazz player (you might not know the former, but if you are reading this blog you surely knew the latter), rhythm is also the linking point between these two forms of art that I enjoy so much, and I've decided to materialize this link in a simple but interesting exercise that will surely help you improve you improvisation skills (or at least give you some fun while you practice your chops).
Ever heard of haikus? Haikus are a japanese short form of poetry, with a pattern composed of seventeen syllabes, divided in three lines (i.e. verses) of 5,7 and 5 syllabes, respectively. How to apply this to music and, more specifically, to jazz improvisation? Well, let's consider bars instead of verses and notes instead of syllabes...and let's use this fixed pattern to improvise. I believe that improvising under certain limitations is a great way of practising, since those limitations force you to enhance your expressivity in order to mantain the interest of your phrases.
If you want to take the haiku concept a step further, you can use the 5-7-5 pattern also to choose your scales. I've been practising this over some blues progressions using a pentatonic scale with a raised 6th substituting the 7th - 5 notes - and a dorian scale - 7 notes -, getting very melodic results. The limitation of notes in each bar forces you to search melodic patterns to fill it, and those scales are rather suitable for that kind of playing. Listen to Robben Ford if you want to find a good example on how to use that pentatonic with a #6, or check out Santana for some nice dorian bluesy licks.