One important aspect of improvising is maintaining rhythmic interest. A well-conceived solo consists of about 70% melodic ideas and 30% running eighth note lines. To have a broad range of ideas, you need to be able to play rhythmically.

Following is an exercise I stole from my book that will provide some practice. This involves playing the rhythm on one note, then with a melodic idea applied. Practice it with a metronome to make sure you don't speed up on the easy parts and slow down on the difficult sections. You could use the second line over an Eb7+4 or A7+4. Try creating your own melodic ideas to use with this rhythm.