Take care — only insiders can do this (4,3)
I believe the answer is:
'take care' is the definition.
(I've seen this before)
'only insiders can do this' is the wordplay.
I cannot really understand how this works, but
'can' could be 'loo' (both can informally mean toilet) and 'loo' is present in the answer.
'do' could be 'ut' (synonyms) and 'ut' is present in the answer.
The remaining letters 'ko' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for look out that I've seen before include "Be on your guard!" , "Beware!" , "A view of the future" , "makes one be careful!" , "as Wenceslas did" .)