If you get a white screen when you launch the app, try this:
(1) Make sure that you have created a start collection (sometimes called a "home" collection), and add that start collection to your top-level nav collection ("default" or "default tablet"/"default phone").
(2) If you selected "Enable Preview" when building the app, make sure that you click the Preview icon to make all your content available. If you did not select Enable Preview, publish your collections and articles.
(3) If it still doesn't work, try uninstalling and reinstalling the app.
One option is to build two apps--one with Enable Preview selected and one with it turned off. Another option is to rebuild the app and turn the Enable Preview option on or off depending on whether you're building the preview app or the production app. Both options work well.