Dance quietly, Jimmy — and don’t start with Jack (6)
I believe the answer is:
shimmy
'dance' is the definition.
(I know that shimmy is a more specific form of dance)
'quietly jimmy and don't start with jack' is the wordplay.
I cannot quite see how this works, but
'quietly' could be 'sh' (both are used to tell someone to be quiet) and 'sh' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for shimmy that I've seen before include "Ragtime dance - gracefully sway" , "Elegantly move" , "Body-shaking dance" , "US ragtime dance - glide effortlessly" , "loose fitting dress" .)