“I dunno, a marketing budget of $0
Incorporate the latest thinking, make sure your designers utilise structured data, and use the latest SEO principles in the actual design.
Try and be different. Why does the world need yet another directory in New York? What are you going to offer that's different to Yelp, Google Local, foursquare or the countless number of directories already out there.
I assume you've done your market research and have found a niche. What is your traffic plan, how will the site be funded? No point putting ads on a site with no traffic, and no business will pay any money for a listing that doesn't stand a chance of either generating leads or have a benefit to their own site.
I genuinely love directories, but it's a different landscape now, than back in 2005 when I started MLS, and even long established directories are failing who haven't moved with the times.
From a standing start, imho you are going to need a decent marketing budget to generate some initial exposure, and then hopefully that will give you traction which you can build on with blogs, SMM etc.
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Yes,

maybe I expect too much for free. Over the years I've learned that you don't necessarily have to charge people to offer them a useful/good service. By using google adsense we can offer our services for free. Of course as you said, until the site lacks traffic, it won't generate any income.
It will be a hard job, but in the last few years we managed to build up some great websites all over the world so we persist in doing it with this new website as well. Just that we need to move with the time ...
Why another directory? Well we all know (if you agree with me

) that competition is ultimately beneficial to the market as well as for users. Even the huge directories can fall if they don't come up with new ideas, plans. If you look at freeindex, how they started and how far they have gotten

Amazing.
Anyway, thanks you for your advice I will stick to it
PS: new comments, opinions, point of views are welcome