Don't trust the default privacy settings. Be sure to check your privacy settings on websites that you plan on using a lot, so that others cannot gain access to you and your information.
Have an exit plan. If someone is bugging or harrassing you online, report them, block them, remove them from chats. You do not have to put up with someone being disrespectful to you online for any reason.
Be just a little paranoid. Do not share your private information with anyone online. Always assume they might be a robot or scam artist phishing for your information to steal your identity.
Stay in safe online spaces. Avoid suspicious websites or videos, since you never know where that link could take you.
Tell someone. It is okay to reach out to administrators of websites when you feel like you have been harassed or feel like something is sketchy about this website.