Be decisive and dump the music practice (3,3,6)
I believe the answer is:
tip the scales
'be decisive' is the definition.
(I've seen this before)
'dump the music practice' is the wordplay.
'dump' becomes 'tip' (as in a rubbish tip).
'music practice' becomes 'scales' (I am not sure about this - if you are sure you should believe this answer much more).
'tip'+'the'+'scales'='TIP THE SCALES'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for tip the scales that I've seen before include "Make the crucial difference" , "name Libra as the probable winner" , "prove decisive" .)