Try, for instance, following rest inside (5)
I believe the answer is:
essay
'try' is the definition.
('essay' can be a synonym of 'try')
'for instance following rest inside' is the wordplay.
'for instance' becomes 'say'.
'following' says to put letters next to each other.
'inside' indicates the central letters.
The centre of 'rest' is 'es'.
'say' put after 'es' is 'ESSAY'.
(Other definitions for essay that I've seen before include "Prose composition" , "Analytic or interpretive literary composition (5_" , "School compeosition" , "Composition; attempt" , "Trial, piece of writing" .)