The red flags I mentioned yesterday on avoiding phone scams (sense of urgency and a request to use a gift card or other cyber currency), might also be vying for your attention if you receive an email that requests payment (known as "phishing").
(2) any attachment from anybody you aren't expecting - don't click the link.
Even if it indicates there's a problem with payment, or your account "needs to be updated." If your bank (or a legit company you've done business with) needs to contact you for anything, they have your phone number and other methods of contact. Or you could always log into said company manually and see if you've received any notifications through their actual web page.