Mean to have grave prepared in AE (7)
I believe the answer is:
average
'mean' is the definition.
(I know that mean can be written as average)
'grave prepared in ae' is the wordplay.
'prepared' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'grave' with letters rearranged gives 'verag'.
'verag' going inside 'ae' is 'AVERAGE'.
'to have' acts as a link.
(Other definitions for average that I've seen before include "Arithmetically ordinary?" , "Run of the mill" , "It's common" , "Mediocre, commonplace" , "'Medium, middling (7)'" .)