Act unwisely and get lost (4,2)
I believe the answer is:
beat it
'get lost' is the definition.
(both can be used to tell someone to go away)
'act unwisely' is the wordplay.
'act' becomes 'beat' (beat is a kind of act).
'unwisely' becomes 'it' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'beat'+'it'='BEAT IT'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for beat it that I've seen before include "make off furtively" , "try out drum kit?" , "leave" , "Scarper" , "Scram, get lost" .)