Quietly increased one's ordinary writing (5)
I believe the answer is:
prose
'ordinary writing' is the definition.
(I've seen this before)
'quietly increased' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'increased' becomes 'rose' (rise can mean to increase or go up).
'p'+'rose'='PROSE'
'one's' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for prose that I've seen before include "Ropes (anag.)" , "Literary genre" , "Ordinary writing" , "Gossipy talker" , "Non-verse" .)