Opening piece very plain and clean, eschewing piano (8)
I believe the answer is:
overture
'opening piece' is the definition.
'overture' can be an answer for 'piece' (I've seen this before). I'm not sure about the 'opening' bit.
'plain and clean eschewing piano' is the wordplay.
'plain' becomes 'overt' (both can mean visible or obvious).
'and' means one lot of letters go next to another.
'clean' becomes 'pure' (similar in meaning).
'eschewing' is a deletion indicator.
'piano' becomes 'p' (musical abbreviation).
'pure' with 'p' removed is 'ure'.
'overt'+'ure'='OVERTURE'
'very' acts as a link.
Can you help me to learn more?
(Other definitions for overture that I've seen before include "Opening music" , "used in attempt to seduce?" , "eg 'The Hebrides'" , "Tentative approach" , "Music played before an opera" .)