You find a new grave in one, usually (2,7)
I believe the answer is:
on average
'one usually' is the definition.
(I've seen this in another clue)
'you find a new grave in' is the wordplay.
'you find' becomes 'one' (I can't justify this - if you can you should give a lot more credence to this answer).
'new' indicates an anagram.
'in' means one lot of letters goes inside another.
'grave' anagrammed gives 'verag'.
'a'+'verag'='averag'
'one' enclosing 'averag' is 'ON AVERAGE'.
Can you help me to learn more?
(Other definitions for on average that I've seen before include "Generally" , "typically speaking" , "Usually" .)