It's critical that you only start negotiations when a company has verbally given you an offer.
Leveling is very important since it’ll dictate your salary band and equity. If you’re at a larger company, ask what level you’re coming in at, and see what kind of wiggle room there is.
If possible, talk to the hiring manager or people involved in your interview"
The above points give you “ammunition” for negotiation: you want to understand how badly the company wants you.