Thumb through book and files before start of election (6)
I believe the answer is:
browse
'thumb through' is the definition.
(I've seen this before)
'book and files before start of election' is the wordplay.
'book' becomes 'b'.
'and' is a charade indicator (letters next to each other).
'files' becomes 'rows' (a file is a row of squares e.g. on a chess board).
'before' is a charade indicator (letters next to each other).
'start of' indicates taking the first letters.
The initial letter of 'election' is 'e'.
'b'+'rows'+'e'='BROWSE'
(Other definitions for browse that I've seen before include "(Of animal) feed on leaves, twigs, etc." , "Read casually" , "Look at various things on the Internet" , "Look through books in bowers" , "Leaf through (a book)" .)