Well exercising due care and attention with emails will keep you out of trouble up to a point. Never open attachments or click links in unsolicited emails, even if they are supposedly from friends, it is easy to fake who an email comes from.
Is the email out of context for the person supposedly sending it you can always check with the friend who supposedly sent it. Take all security/banking/too good to be true emails with a giant pinch of salt. Never open an email attachmnet directly from the email (assuming it comes from a trusted source) save the file to your HDD and scan it with avast, check, check and if you haven't got that check again.