One last point worth mentioning is to try and be the owner of the data that you collect for your application. If you are creating a local shopping/pricing site, then try to create the best database of business information, location and ownership in the area. This data is valuable and can be licensed to others, or made available through an API that brings you more traffic or revenue.
This point can’t be driven home enough. There is very little data/content on Africa available on the web. Whoever captures and creates a database of that information will have an incredibly lucrative product. By the way, this isn’t always easy to do, but then if it was it would already have been done. .