Do NOT open emails and attachments (especially JPEGs, ZIP, PDF, XLS or DOC) from unknown senders. It is extremely likely that these contain malware designed to steal your account details or personal data such as bank details.
Be wary of emails that appear to be from people you know but contain content that looks suspicious or out of context. Often malicious emails will 'spoof' a persons email address to make it appear that an email is from the designated sender when in fact it is from a completely different email address.
For further information see: