Practice somewhat beneath him at first (5)
I believe the answer is:
habit
'practice' is the definition.
(habit is a kind of practice)
'somewhat beneath him at first' is the wordplay.
'somewhat' becomes 'abit' (a bit).
'beneath' means one lot of letters go next to another (in a down clue).
'at first' indicates taking the first letters.
The first letter of 'him' is 'h'.
'abit' after 'h' is 'HABIT'.
(Other definitions for habit that I've seen before include "Monk's robe or repetitive action" , "It's worn in order" , "Riding garment" , "Settled tendency" , "Routine - clothing" .)