Move fast! Don't do this with something unpleasant! (4,2,2)
I believe the answer is:
step on it
'move' is the definition.
(I know that step on it is a type of move)
'fast don't do this with something unpleasant' is the wordplay.
I cannot really understand how this works, but
'something' could be 'it' (I've seen this in other clues) and 'it' is found within the answer.
The remaining letters 'stepon' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for step on it that I've seen before include "Hasten" , "to take advantage of escalating opportunity" , "Be quick" , "improve rate of advance" , "How might one kill an ant" .)