What should you know before starting work?

I was told: HR works for the company and not you. Don't gossip as it would be used against you. Don't make friends just be polite. Don't do work that's not in your job description.

I want to know if there is anymore tips I should know before going into the workplace. I just want to know how your co workers or company can screw you over so I don't get screwed over.

Thanks.