Best get up before one, working for a drink (6)
I believe the answer is:
potion
'a drink' is the definition.
(potion is a kind of drink)
'best get up before one working' is the wordplay.
'best' becomes 'top' ('top' can be similar in meaning to 'best'**).
'get up' says the letters should be written backwards.
'before' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'working' becomes 'on'.
'top' back-to-front is 'pot'.
'pot'+'i'+'on'='POTION'
'for' acts as a link.
(Other definitions for potion that I've seen before include "curative drink" , "Drink, maybe medicinal" , "Medicinal draught" , "Magic concoction" , "Drink, maybe philtre" .)