The two most common ways of getting into someone else's account:
1) Phishing. They sent out a mass email to people that looks legit, telling them that they need to click on a link and log into their GoDaddy account. You click on the link and then enter your login and password. They now have your credentials.
The only way to prevent this is to question everything. Your best bet is if you get an email saying go to GoDaddy and log in - open up your browser and type in godaddy.com and log in or call their customer service. Do not click on any link in an email.
2) Hacking emails. Free email services are not hack proof. It's not easy but it's not impossible. They hack it and set up an invisible forwarder to send your emails to another account. Then, they go to your registrar and request a password reset.
Using an email based on one of your own domains adds another level of security. They'll need to get into your account to set up the forwarding (and by then it'll be pointless because they're already in). No simple hack and get the password.
Also, make sure your passwors are secure. Don't use common ones - loved ones, pets, hobbies, etc. Non native languages are good, non alphanumberic characters ($*&) are good, even non-traditional characters ( ñ, ÿ, ô, ¿) are good to have, too.
If you have to use one of the common ones, don't just have the word. If you like soccer and want to use that as your password, then make that secure. $0cc3r would be far more secure than just soccer.