Superior, negative, but safe advice (6,3)

I believe the answer is:

better not

I'm a little stuck... Click here to teach me more about this clue!

'safe advice' is the definition.
I know nothing about this answer so I can't judge whether this works.

'superior negative' is the wordplay.
'superior' becomes 'better' (better is a kind of superior).
'negative' becomes 'not' (I've seen this in another clue).
'better'+'not'='BETTER NOT'

'but' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.