Best prepare for exam about English (5)
I believe the answer is:
cream
'best' is the definition.
(as in 'the cream of the crop')
'prepare for exam about english' is the wordplay.
'prepare for exam' becomes 'cram' (cram can mean to revise for an exam).
'about' means one lot of letters goes inside another.
'english' becomes 'e' (abbreviation).
'cram' placed around 'e' is 'CREAM'.
(Other definitions for cream that I've seen before include "Thick milk" , "Beat" , "best people" , "Elite; pale yellow" , "Milk product" .)