Advice to new jazz singers

Singers: practice with playalong tracks by singing the melody over and over, each time with slight variations. But how do you decide what and how to change? Pay attention to the lyrics. Find a special word, and try singing it a) suddenly louder b) suddenly softer c) longer d) shorter e) with a rougher timbre f) with a scoop or slide g) with a melodic ornament h) with a rhythmic pattern you hear in the drums i) with a different pitch you hear from the piano j) etc., etc., etc. Do this for the whole length of the playalong. Do it again. Take a break and do it a couple of times tomorrow too. And the next day. 

Over time you may find yourself settling into a certain interpretation that is unique to you. You created it -- composed it -- through improvisation. Feels good, doesn't it?