Maths AA HL preparation

I’m doing Maths AA HL next year.

Right now I’m doing IGCSE international maths 0607.

What did you wish you knew before starting this subject?

What topics did you wish you had stronger bases on?

What are some topics I can learn a bit on my own so I can be more ‘advanced’ and already prepared while I’m in class?

I’ve tried to post this multiple times but it doesn’t go…