When you are registering a domain name as a webmaster you must be very careful at the time of registering. First of all make sure your domain name's spelling is correct. Secondly select the desired domain extension as .com, .org or any other you wish. Like wise you must give your original and primary email address. Because when the domain is going to expire or any legal notice will be sent to this e-mail. If you didn't respond to the mail you may loose your domain. That's why it is important to use your primary e-mail as it will help you to view the notices in time and you can take necessary actions.
Also you must know that when registering the domain don't forget to give your true contact information like address, phone number. Failure to do so may end in Losing your own domain.