Don't use the same username everywhere (so people can't just look you up and find you all over the place). Change it where you can and delete old accounts you're not using. Don't use the same profile pics or bios across accounts. Go through privacy/security settings and make sure you turn off any location stuff and turn off anything that lets you get suggested to phone contacts. Private EVERYTHING! Remove age, birthdays, your real name (obviously), etc. Clear all history, factory reset your computer.