Building community would always depend on your project. If your project offers a really good deal to solve something or to make an impact in one's life, I'm sure it will be appreciated by the people you want to attract and to help. For me, Storytelling is one way. You have to spread your cause. Rally people to believe in your project and to help you deliver your mission. It's imp that you know who they are and where can you find them. Sure, you can always offer airdrops, bounty, and other stuff but the thing about building community is about the retention of these people.  So, I suggest that you let your community grow, organically with the people who really support your project not just spending on it. Acquiring members is kinda manageable but I think what you also need to focus on is how to retain them.