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You got to give in order to get. And in this case, the community wants you to do a lot of giving before they trust you. This is a difficult line to walk. Here is an idea. Put a video up on YouTube showing how to use your app. Personally I think it would be good to hire a booth babe to star in the video. But that's just me.
Before you run out and code your app, make sure you have a purpose. Write it down. That way you have a concrete goal. And it will show in the app you churn out. Good stuff. Now go and write that useful app. If you build it, they will come.