Creep furtively ahead of reverend, one in seat for private screening (5,7)
I believe the answer is:
sneak preview
'private screening' is the definition.
'sneak preview' can be an answer for 'screening' (sneak preview is a kind of screening). I'm not certain of the 'private' bit.
'creep furtively ahead of reverend one in seat' is the wordplay.
'creep furtively' becomes 'sneak' (I've seen this in another clue).
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'reverend one in seat' becomes 'preview' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sneak'+'preview'='SNEAK PREVIEW'
'for' is the link.
Can you help me to learn more?
(Other definitions for sneak preview that I've seen before include "Unannounced screening" , "Test screening before general release" , "Private screening or viewing of new film etc." , "Public showing of a film before general release" .)