Decoration is routine with group (7)
I believe the answer is:
rosette
'decoration' is the definition.
(rosette is a kind of decoration)
'routine with group' is the wordplay.
'routine' becomes 'rote' (I've seen this in another clue).
'with' means one lot of letters goes inside another.
'group' becomes 'set' (both can mean a collection).
'rote' going around 'set' is 'ROSETTE'.
'is' is the link.
(Other definitions for rosette that I've seen before include "Political supporter's ribbon" , "Party wear" , "Horse show award" , "collection of ribbons" , "sign of support for party" .)