Most of the common guidelines already Rakib mentioned , thanks for your work rakib . ( Both of our native language is Bangli, so writing quality of us is not up to the mark, I expect all will pardon us
.
if some one is really new , he'd better learn from experts , go to dmoz, yahoo , take a look how they organise sites.
When u add any site in any category ask yourself , does the site really fit in the category, do you think the visitors will find the site really useful, for such site do you think visitors will look in the category you are adding it
if needed create new category with proper description which sites you expect here ,