Step but first to peruse (5)
I believe the answer is:
tread
'step' is the definition.
(I know that tread is a type of step)
'first to peruse' is the wordplay.
'first to' becomes 't' (1st letter of 'to').
'peruse' becomes 'read' (I've seen this before).
't'+'read'='TREAD'
'but' is the link.
(Other definitions for tread that I've seen before include "Tramp" , "Step (heavily)" , "Gripping part of tyre" , "Walk or step like pattern on tyre" , "March" .)