Shorten it do, stupid! (8)
I believe the answer is:
condense
'shorten' is the definition.
(condensing is a kind of shortening)
'do stupid' is the wordplay.
'do' becomes 'con' (both can mean to defraud).
'stupid' becomes 'dense' (similar in meaning).
'con'+'dense'='CONDENSE'
'it' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for condense that I've seen before include "Change from vapour to liquid" , "Abbreviate" , "precis" , "contract?" , "Send once (anag.)" .)