Once you can play the scale in this manner without losing the rhythm, try memorizing the rhythm on one note first, and then improvise with it. Play any notes from the scale in any order you like, but be sure to keep the rhythm exactly the same every bar. This example demonstrates four bars of an improvised melody using a set rhythm.
The next step is to move the quarter note to the second beat and play eighth notes in the rest of the bar. Once again, memorize the rhythm and then improvise with it. Then repeat the process with the quarter note on the third beat of the bar, and then again on the fourth beat of the bar.
It is also worth learning to improvise with a constant stream of eighth notes. This is difficult at first, because you get no time to think ahead between notes. However, if you work at it you will find that it gives you more control over your improvising in general. The next example includes four bars of improvisation using constant eighth notes.