One of the main concerns should be to play melodically. This does not necessarily mean playing cute, but there needs to be some sense of continuity for your melodic lines, and they need to be interesting in themselves. You also need to be aware of the rhythmic and harmonic development of your improvisations; I include these concepts in the expression “melodic development”. This is difficult to teach, and it is probably the aspect of improvisation that requires the most creativity. Anyone can learn the relationships between chords and scales; what you do with that knowledge is what determines how your music will sound.
There are some common ways that can be used to structure the solo. One of the most important is repetition. After a soloist plays a phrase, he often repeats it, or a variation on it. Usually the phrase, or the variation, is played three times before moving on to something else. The variation can be carrying the phrase, or changing important notes within it to conform the phrase to a new chord / scale. The variation may simply consist of starting the phrase at a different point in the measure, such as the third beat instead of the second. The phrase itself can be changed rhythmically, playing more slowly or faster.
