Most webmasters can't resist the allure of directory submissions. Simple spend a little bit of time and effort completing the directory submission form, and poof: an inbound link to your site appears on the page. While directories are an easy way to collect inbound links to your site, not all directory links are worth their weight. If the directory has a lower page-rank than your site, the link is unlikely to boost your page-rank. Similarly, if the directory is not especially relevant to your niche, a link isn't going to make a significant impact on your website's ranking with the search engines.
To get the most from your directory submissions, you must laser in on two criteria: relevancy and page-rank. When evaluating directories, first consider the relevancy of the site. Is the directory linking exclusively to pages within a specific niche or is it linking to every kind of site under the sun? Once you've found directories that are relevant to your niche, evaluate the page rank of these directories and submit only to those with a higher page-rank than your site. If there are multiple categories to which your site could belong, choose the category that has the highest page rank. Consider relevancy first, page rank second, because if your site isn't relevant to the category, it's unlikely to be accepted anyway.
By choosing directories (and the target category) based on page-rank and relevancy, your inbound links from these sites will have more weight with Google and do more to boost your page-rank.
