Jazz Improvisation Tip: A song's chord changes, harmonic substitutions, patterns, rhythmic devices, etc. can at times be cart before the horse. Lyrics and melody go out the window.
The American songbook hasn't gone out of style. Recite the words as lines of poetry. Deal with melodic content of the song for as long as you need in order to get in touch with your timing, tone, articulation, and stylings.
Nat King Cole is your homework.
Peace & Keep Swinging,
Andre Hayward