Excellent advice - the best (6)
I believe the answer is:
tiptop
'excellent' is the definition.
(I've seen this before)
'advice the best' is the wordplay.
'advice' becomes 'tip' (a tip is a piece of advice).
'the best' becomes 'top' (top can mean the very best).
'tip'+'top'='TIPTOP'
(Other definitions for tiptop that I've seen before include "Excellent, super" , "cracking" , "First-class" , "First-rate" , "The pinnacle of perfection" .)