I have found the best way to test usability and watch "real world" user flow is to put the product in the hands of someone who is not tech savvy (girlfriend, wife, mom, drunk friend, etc) and watch them interact with your app. Sometimes I may choose to give them a brief overview of what the app sets out to accomplish, other times I let them figure it out themselves. There's many ways to skin a cat but I find this to be the simplest and most effective.