Instruction not to wear so much (6)
I believe the answer is:
lesson
'instruction' is the definition.
(I know that lesson is a type of instruction)
'not to wear so much' is the wordplay.
'not' becomes 'less' (I've seen this in other clues).
'to wear so much' becomes 'on' (I can't justify this - if you can you should give a lot more credence to this answer).
'less'+'on'='LESSON'
Can you help me to learn more?
(Other definitions for lesson that I've seen before include "Instructive experience" , "Seminar" , "Severe reproof" , "What teacher provides" , "Teaching session or Bible passage" .)