Model intoxicated? Take no action (3,5)
I believe the answer is:
sit tight
'take no action' is the definition.
(I've seen this in another clue)
'model intoxicated?' is the wordplay.
'model' becomes 'sit' (e.g. for a painting).
'intoxicated?' becomes 'tight' ('tight' can be similar in meaning to 'intoxicated').
'sit'+'tight'='SIT TIGHT'
(Other definitions for sit tight that I've seen before include "Remain firmly in place, take no action" , "Refuse to be diverted" , "Maintain one's seat" , "Remain firmly in one's place" , "Keep one's position" .)