Decorate for a party with sailors (5)
I believe the answer is:
Here is my best explanation:
'decorate' is the definition.
('adorn' can be a synonym of 'decorate')
'a party with sailors' is the subsidiary indication.
'party' becomes 'do' (do is a kind of party).
'with' says to put letters next to each other.
'sailors' becomes 'rn' (abbreviation for Royal Navy).
'for' is the link.
(Other definitions for adorn that I've seen before include "get dressed!", "Deck", "Embellish, decorate", "Improve appearance", "Make more attractive", "Bedeck", "dress", "Festoon", "Beautify - decorate - enhance" and "Dress".)