Do not submit any site which is not finished. Make sure all your cgi is running properly. Make sure your website is viewable in both MSIE and Netscape. You have no guarantee what browser the reviewers will use. Make sure you've read their FAQ and have met all of their requirements concerning submissions.
Content is king.
This means that a website selling Gizmos is more likely to be accepted if you take the time to explain why your gizmos are better than your competition. A site selling gizmos without the content is not as likely to be accepted as a site which takes the time to educate the visitor. It's key to understand that your effort is rewarded by inclusion into the directory. If you fail to be accepted, go back and review your site. Ask some friends or customers, and use the feedback to rework the site.