See a wild tit's come in and don't move (3,5)
I believe the answer is:
sit tight
'don't move' is the definition.
(I've seen this before)
'see a wild tit's come in' is the wordplay.
'see' becomes 'sight' (I've seen this before).
'a wild' indicates anagramming the letters.
'come in' means one lot of letters goes inside another.
'tit' anagrammed gives 'itt'.
'sight' going around 'itt' is 'SIT TIGHT'.
'and' is the link.
(Other definitions for sit tight that I've seen before include "Maintain one's seat" , "Wait and see!" , "Go nowhere" , "Be too drunk to stand?" , "Keep one's position" .)