This video discusses 5 ways to keep your app popular after launch.
Provided you have done your pre-launch marketing correctly, a new app on the app-stores can drive a lot of interest, and as a result, downloads appear high in the first couple of days.
But don't think this will last forever!
Users are fickle creatures and lose interest quickly. It is up to you to have a strategy in place that will keep your app popular with your users long after the initial launch.