Heading across France occasionally to find grave (7)
I believe the answer is:
earnest
'grave' is the definition.
(I've seen this before)
'heading across france occasionally' is the wordplay.
'heading' becomes 'east' (heading can mean a compass point or direction).
'across' indicates putting letters inside.
'occasionally' means one should take alternating letters.
The alternating letters of 'france' are 'rne'.
'east' placed around 'rne' is 'EARNEST'.
'to find' acts as a link.
(Other definitions for earnest that I've seen before include "Serious - down payment" , "'Serious, sincere (7)'" , "businesslike" , "Sincere -- humourless" , "Showing sincere and intense conviction" .)