Your online accounts are already gold for hackers. Don't make them goldmines.
Never email your Social Security number, because it'll stay in your archives. Erase old messages with your bank account information and credit card numbers. And never keep a saved document that serves as a master list of passwords. For hackers, that's a treasure map.
And if you keep nude photos or other sensitive information, just because you deleted it doesn't mean it's gone forever -- there might be a cloud backup. Know where your data is being saved.