This document discusses various ways to monetize mobile apps, including direct sales through app marketplaces or a website, advertising revenue within apps, in-app purchases, and cross-promoting other apps. It provides tips on building apps for different device types and platforms, marketing apps through social media and advertising platforms like Google AdWords and AdMob, targeting demographics, and using analytics to improve user retention and sales. Results from advertising one developer's app showed spending $8-10 to make $2-4 per app in ad revenue. Combining advertising with other techniques was recommended to boost apps in marketplaces.