Piece of advice: crock should reverse to get to A1 (6)
I believe the answer is:
tiptop
'to a1' is the definition.
'piece of advice crock should reverse' is the wordplay.
'piece of advice' becomes 'tip' (I've seen this before).
'crock' becomes 'pot'.
'should reverse' shows that the letters should be reversed in order.
'pot' reversed gives 'top'.
'tip'+'top'='TIPTOP'
'to get' acts as a link.
(Other definitions for tiptop that I've seen before include "The very highest point" , "Quality" , "Informally excellent, very best" , "Excellent, super" , "Capital" .)