Excellent advice when on Jersey? (6)
I believe the answer is:
tiptop
'excellent' is the definition.
(I've seen this before)
'advice when on jersey?' is the wordplay.
'advice' becomes 'tip' (I've seen this before).
'when on' is a charade indicator (letters next to each other).
'jersey?' becomes 'top' (type of garment).
'tip'+'top'='TIPTOP'
(Other definitions for tiptop that I've seen before include "Best of its kind" , "Informally excellent, very best" , "The very highest point" , "First-class" , "First-rate" .)