Start to show to advantage (3,3)
I believe the answer is:
I believe this clue is a double definition.
'start' is the first definition.
(I know that set off is a type of start)
'show to advantage' is the second definition.
(I've seen this before)
'to' acts as a link.
(Other definitions for set off that I've seen before include "Depart" , "Begin journey or cause to ignite" , "radio with no reception" , "Display - mount - start journey" , "show to advantage" .)