First to order drink after a month shows proper behaviour (7)
I believe the answer is:
decorum
'proper behaviour' is the definition.
'decorum' can be an answer for 'behaviour' (decorum is a kind of behaviour). I'm not sure about the 'proper' bit.
'first to order drink after a month' is the wordplay.
'first to' says to take the initial letters.
'drink' becomes 'rum' (rum is a kind of drink).
'after' means one lot of letters go next to another.
'a month' becomes 'Dec' (abbreviation for December).
The initial letter of 'order' is 'o'.
'o'+'rum'='orum'
'orum' after 'dec' is 'DECORUM'.
'shows' acts as a link.
Can you help me to learn more?
(Other definitions for decorum that I've seen before include "Protocol" , "Seemly behaviour" , "(Of outward appearances) what is proper" , "modesty" , "Dignity of behaviour or procedure" .)