One of the problems facing app producers at the moment is getting seen. This is especially so with paid apps because users usually look for a free app first and might not even search for a paid app. Most developers tend to create a demo or lite version of their app that helps alleviate this problem. However, people will still only find you if they have searched for your type of application. There’s no serendipity that allows your app to be found accidentally.
One solution is to join an ad network such as AdMob. You can place ads that will be shown in other applications on the same OS platform. However, with today’s low app prices, it’s likely that you will pay more for advertising than you might gain through selling your app!
Another solution is to write some unrelated, useful free apps yourself and use them to cross-promote your paid apps. I do this with my own Android freeware applications (with over 120,000 installs) and they are currently promoting my paid Android Database app.
Larger companies such as Zumobi also use this technique to cross-promote between popular paid apps…
"As a publishing network, we can cross-promote aggressively all of our applications," Willner says. "For example, you’ve downloaded our Motor Trend App; we will also suggest our NASCAR app — very, very big advantage and frankly something the two guys in the garage can’t take advantage of."
… although "two guys in a garage"… can do something similar by writing some useful free apps.