I agree with what's said here, and that it's tough. I have an iphone time tracking app and here are my sales http://seriouslackofdirection.blogspot.com/2013/01/my-app-st...

I also suggest:

-changing the price (price reductions shows up on app tracker apps and twitter feeds).

-get good reviews from your friends.

-you might look into app store keyword optimization also.