Took to be the done thing (8)
I believe the answer is:
accepted
'took' is the definition.
('accept' can be a synonym of 'take')
'be the done thing' is the wordplay.
'be' becomes 'accept' (accepting is a kind of being).
'the done thing' becomes 'ed' (I can't justify this - if you can you should believe this answer much more).
'accept'+'ed'='ACCEPTED'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for accepted that I've seen before include "Believed to be valid" , "Taken" , "such behaviour normal?" , "Tolerated; believed to be correct" , "Received something offered" .)