One of the most important aspects of jazz music is improvisation. Jazz singers nowadays are becoming more and more a "team player" by taking part on the instrumental Improvisations. While saxophones and trumpets are shining on their solos, singers can learn how to do it as well. If you want to learn the jazz language and communicate it to your audience, the best way to do it is to transcribe-analyse and re-enact (imitate) solos of horn players and singers. By doing this in multiple solos and adding the syllables that fit better your vocal character, you will develop the language for jazz improvisation. Here is a simple modal jazz solo by Miles Davis on his brilliant composition "So What".
7 steps that will improve your improvisation singing skills
Find a solo that you really like preferably by horn players or singers.
Listen to it carefully. Better with headphones.
Slow it down and sing it with the recording until you know it on the regular speed.
Use "scat" syllables that feel natural to you or check what other singers use and adopt what you like.
add phrasing! which includes, how the language is used and pronounced. The rhythmic feel, the interpretation of the beat, expressive techniques & dynamics, articulation, as well as the use of expressive nuance in one's sound.
transcribe/notate phrase by phrase & analyse it.
Use the solo as a starting point to improvise and start creating your own ideas.
In my opinion transcription is one of the most efficient and productive techniques for learning to improvise in the jazz tradition. After transcribing multiple solos you will realise that you have gain musical freedom, artistic creation and hopefully a recognisable style of singing. Learning from the past is the only way to evolve. Imitation in the process of learning is timeless and inevitable.
Suggested solos to start with
Do it the Hard way-solo of Chet Baker
It could happen to you solo by Chet Baker
Moanin’ solo by Karrin Allyson
Take the A train solo by Ella Fitzgerald
All of me solo by Sarah Vaughan
Someday my prince will come solo by Miles Davis
How high the moon solo by Ella Fitzgerald
Anthropology solo by Sheila Jordan