Hi Markas,
If your goal is to be running a high-quality Yellow Pages-type directory for the Baltics, then it's a good start to get as many businesses as you can into your index. Things that will improve the authority of your directory might include:
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Getting business owners to take control of their listings and add their own details to them, including business descriptions, hours of operation, payment forms accepted, parking available, credentials, years in business, website address, photos etc. Take a look at Google+ Local listings, YP listings, Yelp Listings and see the types of information being included on the individual listings to make the rich sources of information.
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Harness UGC. Become a review platform and enable customers to review their favorite business, the way sites like Yelp and TripAdvisor do. This will build up the unique, useful content on your directory with nearly all of the work being done by members who use the directory and want to review businesses they patronize.
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Form relevant partnerships. In the world of YP and local business indexes, a lot of data changes hands. Take a look at the relationships documented in Get Listed's Local Search Ecosystem infographic and you will see how different players team up to share data: https://getlisted.org/static/resources/local-search-data-providers.html. Unfortunately, I don't have any first-hand experience with the local business scene in the Baltics, but if you can identify partners, you can help one another build authority.
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Then, there is the obvious: making sure your directory is search engine friendly. Be sure all important URLs can be crawled and that your navigation system is easy to use. Be sure you've got good basic content on your site (contact page, about page, policy pages, etc.) and then see what else you can build that will make your directory site unique and useful. Be sure you've covered the basics of on-page SEO to make your pages as clear as possible to search engines and human users.
These are just a few ideas. I think the main thing here is for you to study how other directories have gone from being small-time to becoming major players. If there aren't currently a ton of well-established local business indexes in your geography, you may have an exciting opportunity to become a major player. It really depends on the competition. Study local competition and look at the big guys in countries like the US to see what makes them tick. Hope this helps!