Timid at first, I'm on song, getting a drink (3,5)
I believe the answer is:
tia maria
'a drink' is the definition.
(I've seen this before)
'timid at first i'm on song' is the wordplay.
'at first' indicates taking the first letters.
'i'm' becomes 'iam' (I've seen this in other clues).
'on' is a charade indicator (letters next to each other).
'song' becomes 'aria' (aria is a kind of song).
The initial letter of 'timid' is 't'.
't'+'iam'+'aria'='TIA MARIA'
'getting' acts as a link.
(Other definitions for tia maria that I've seen before include "Coffee-flavoured trademarked liqueur" , "Coffee-flavour liqueur" , "Coffee-flavoured rum drink" , "Rum-based coffee liqueur" , "Coffee-flavoured Caribbean liqueur" .)