Follow first of guests after party (3)
I believe the answer is:
dog
'follow' is the definition.
(dog can mean to follow or torment)
'first of guests after party' is the wordplay.
'first of guests' becomes 'g' (1st letter of 'guests').
'after' means one lot of letters go next to another.
'party' becomes 'do' (do can informally mean a party).
'g' put after 'do' is 'DOG'.
(Other definitions for dog that I've seen before include "Worry" , "Canine animal" , "boxer?" , "'You cannot teach an old ... new tricks'" , "A pet; its life prov. wretched" .)