What makes a good directory? This is two different topics to be pointed at two different perspectives - directory owners and directory users/submitters. There have been many threads on what makes a good directory and what does not. Many of the items below may have been covered in those.
Directory owners (taken from my own directory tips pages):
Use "Good" Hosting Services
If you cannot afford $25-60 or much more (depending on your requirements) a month to invest in something that can return that amount of money 10-100 times and more per month in the coming years, then you really need to rethink your business model. Directories are not "get rich quick" sites and to succeed you need to offer something different, execute it well, and stick with it for the long term to be really successful. Finding a really good host is one of the first steps to being successful.
Charge a nominal fee
Many do not agree with this, but my opinion is to always charge a nominal fee. If you do not, you will be spammed to death no matter what kind of "word" filters your script may have. If I'm going to list sites for free - I will be the one to choose the best sites. Plan to spend 10-15 minutes reviewing and looking at the site. Write the title and description following the principles you plan to adhere to throughout your directory.
Plan, plan, plan
Think of how your directory can grow and allow for easy/useful navigation throughout. Niche subject/topic directories are the easiest to build and work on. There are enough general directories out there and 99.9% of them are worthless to the user. Look at the topic, look at the competition, do something different!
Don't launch prematurely.
There is nothing worse than an empty directory to both the search engines and the users.
Also, if you are going to seed it using dmoz etc.
1. do not use every listing in a category as seed - choose a small sample
2. change all titles and descriptions (actually review the site)
3. decide on a link, anchor, or title format and stick with it (don't give anchor text just because someone requests it if it doesn't fit your titling format)
Don't Generate a Directory Based on Your "Planned" Taxonomy
Meaning, don't generate a bunch of empty categories. It is quite simple to have an add URL link on the upper level category. For instance if you have a regional directory of the United States and you have each state but not every locality you simply state that localities will be created as necessary and simply allow them to submit to the State and then create localities as needed.
Don't Run AdSense Right Away
Once a directory becomes established, advertising of this nature may be an option, but not at launch or anytime shortly thereafter until you gain traffic.
Don't Solicit Advertising Right Away
Once a directory becomes established, advertising may be an option, but not at launch or anytime shortly thereafter until you gain traffic. My rule is to wait until you are contacted about advertising before placing any of the advertising options on the site. Using this approach almost guarantees you have stirred enough interest with potential advertisers.
Keep It Out of the SEO Spotlight
Nothing's worse than building a "link" directory catering to SEO's. Keep it out of those circles or you may as well put an image of a bull's-eye for your homepage as far as Search Engines go.
Don't List Email Addresses
Never list email addresses of the listings, no matter what. Your site will only become a spam magnet for email harvesting robots/users. Yes, you can block these robots using .htaccess, but don't subject your submitters to getting spammed from this.
Stick to your principles
Don't be afraid to reject submissions and refund money. Don't accept mirrors or any other trash you don't feel good about. Again, stick with a format for titles/descriptions whatever that may be - don't let the submitter spam out their title/description with keyword, keyword, keyword, keyword, keyword, keyword, keyword, keyword, repeated throughout the listing/advertisement.
Building a "useful/successful" directory that will be around for years and survive search engine algo changes etcetera takes knowledge of the subject, knowledge of taxonomy, interest in the subject, and time - lot's and lot's of time. I always suggest building on a topic in which you are familiar with and interested in, not based on the cost of keywords in the PPC market. Plan it well and don't rush it.
[edited by: Webwork at 4:40 pm (utc) on Oct. 9, 2006]
[edit reason] Split Thread - Excellent Work - Deserves Own Thread [/edit]