There are now 200,000+ apps in the app store and the days of build it and they will come are over. However, the opportunity still exists on the iPhone and other mobile platforms, mostly Android but you need to know how to get found.   

1) Name your app well. Search in the app store is poor and it seems the app name carries a lot of weight in the search so pick a name that includes your keywords.

2) Get your app rated. The more ratings you get the more people will download your app. I saw sales almost double on 1 app after getting users to rate

3) Use the web to promote your app. If you have an audience on Facebook, Twitter, your blog, or any other web site, I’ve found that to be a great way to drive people to the app store

4) Hit the blogosphere.

5) Buy some clicks on admob or other ad networks which let you target by OS and browser