I wrote about how we use side projects to attract pretty high value clients for our unlimited UI design service. You can read about our strategy here: <a href="https://www.reddit.com/r/Entrepreneur/comments/6ztybx/how_i_attract_high_paying_clients_to_my_design/" rel="nofollow">https://www.reddit.com/r/Entrepreneur/comments/6ztybx/how_i_...</a>
That heavily depends on your stage. In the seed and early stages it is about you as the founder who can sell the product the best. Network like crazy, go for long lasting relationships and make your first customers very happy. For any other stage and business model, you have to ask more specifically / provide more details about your business as the sales funnel & buyers journey can vary a lot.