This is a good article on 10 ways to spot email scams:
http://www.switched.com/2009/10/26/10-ways-to-spot-an-e-mail-scam/
Anyone asking for personal information, credit card information or saying you won money via email is probably a scammer. Remember not to click links in emails unless you are sure they are legitimate. Also remember scammers can pretend to be a trusted source. Check the article for the top 10 ways to spot email scams. If in doubt, delete the email without opening it.

You can also use NoLuckNeeded's list of known email scams to protect yourself:
http://www.noluckneeded.com/beware-new-scam-emails-phishing-scam-emails-spam-list-t7866.html