Get up on piano and show off (10)
'show off' is the definition.
'get up on piano' is the wordplay.
'get up' becomes 'stand' (I've seen this before**).
'on' means one lot of letters go next to another.
'piano' becomes 'grand' (grand piano is a kind of piano).
'stand' after 'grand' is 'GRANDSTAND'.
'and' is the link.
(Other definitions for grandstand that I've seen before include "Such a good view", "Terraced block of seats commanding the best view of a sporting event", "From which spectators watch", "Racecourse construction", "Show off in America".)