It makes perfect sacrifice, deed being hidden (8)
I believe the answer is:
practice
'it makes perfect' is the definition.
(I've seen this before)
'sacrifice deed being hidden' is the wordplay.
'sacrifice' becomes 'price' (I can't explain this - if you can you should believe this answer much more).
'deed' becomes 'act' (an action).
'being hidden' means one lot of letters goes inside another.
'price' enclosing 'act' is 'PRACTICE'.
Can you help me to learn more?
(Other definitions for practice that I've seen before include "Habit - procedure" , "Doctor's business" , "Exercise; professional business" , "''. . . . . . . . maked perfect''" , "Customary procedure" .)