How would one go about suing in cases like this?

You would start by reading the complete terms and conditions of service. Somewhere in there is a paragraph that states that your account can be suspended and/or terminated at any time for any reason, or no reason. Then you find the paragraph that limits you to mandatory arbitration. You conclude that you're wasting your time if you attempt to sue anyone over this. Eventually you realize that you're better off without a FB account.

For any legal action you should find a lawyer. Many lawyers will be happy to meet briefly with someone to figure out what they can do for you or if they should point you to somebody else. In this case such a meeting is likely to be very brief indeed, the chance of success is negligible and the likely costs are sky high.