Attach present advertisement first (6)
I believe the answer is:
adhere
'attach' is the definition.
(adhering is a kind of attaching)
'present advertisement first' is the wordplay.
'present' becomes 'here' ('here' can be similar in meaning to 'present').
'advertisement' becomes 'ad' ('ad' can be a synonym of 'advertisement').
'first' is a charade indicator (letters next to each other).
'here' after 'ad' is 'ADHERE'.
(Other definitions for adhere that I've seen before include "Hold fast, stand by" , "Stick like a stamp" , "Stick or cleave to" , "Remain attached" , "Stick to or continue faithful" .)