Answer:
Listing your personal information (phone number, email address, etc.) no one should know you personal information except you
Posting any inappropriate photos - not every wants to see that. Or you don't want everyone to see that
Forgetting to limit who can see your posts- Letting anyone and everyone see your posts
Vacation details to more than close friends- Why would you want strangers seeing where you will be staying
Credit card or financial information- People can steal you personal information if you post it on social media