Maybe don’t fancy this immediately? (4,4,4)
I believe the answer is:
just like that
'maybe don't' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'fancy this immediately?' is the wordplay.
I cannot really see how this works, but
'fancy' could be 'like' (both can mean to find someone attractive) and 'like' is found within the answer.
'immediately?' could be 'just' ('just' can be a synonym of 'immediately') and 'just' is found within the answer.
The remaining letters 'that' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for just like that that I've seen before include "have only a single preference" , "right away" , "straight away" , "Simply so! - Tommy Cooper's catch phrase" , "Out of the blue" .)