Improvisation is common in many types of music, but is mainly expressed in jazz. Most all players know a common set of songs called standards. These standards are know by all and can be called on at any time in a concert . A player can expect to build his own solo jazz part upon a standard usually. If you plan to be a instrumentalist, you definitely should attempt to learn the jazz standards. Only after you know the song and its chordal structure can you be an effective soloist . Reading music can be an invaluable skill when it comes to this task.
The instrumentalist usually will not begin prior to the main melody of the song being played once through by everyone. Awaiting your cue to begin your jazz solo, you are well advised to know how long the first section will be. You will receive a nod by the leader of the band to begin your solo when it is your time in any case. Often your solo will begin after the singer finishes the verse and chorus.
Only understanding and a good understanding of musical structure will be the building blocks of a great jazz improvisations. The chord pattern of the song dictates the boundaries of your solo. This is where all the time you spent practicing scales will bear its fruit. Learn the scales in all keys and go from one to another with a seamless transition and you will learn to build a good jazz improvisation. If you find it difficult at first to build a solo, try playing arpeggios in the key signatures as you move through the song. A solo is not just running scales however. The jazz solo should contain dynamics, structure and have something to say. You cannot know the exact way you will get through your solo, but you can know generally how you will get there.
Most jazz improvisations start with at least a general understanding and statement of the melody. Starting simply is the best way to leave room to move as you go through your solo. As you go on through your solo you can increase the tension, dynamics and tempo before resolving to the main melody at the end. If you examine some of your favorite solos, you will see that more often than not they follow this general structure .
Listen to other soloists to hear how they do their jazz improvisations. Go to concerts, buy recordings and learn how to build your own jazz musical solo. In time you will know what the structure of a good jazz improvisation is intrinsically without being told.