Great question! I eager to hear people's experiences as I will be in this position in a few months. So far my approach has been to proactively build audience awareness. I feel driving people to your product is important. To me apps are in a bit of similar situation to novels (which I also write, publish, and sell via distributors/retailers). There are many books and many apps. Raising awareness, especially through word of mouth, helps bring customers to you. A much lower number of people are going to stumble across an app (or book) through key word searches. The retailers don't have much interest or incentive to work with small indies unless you manage to build a big audience on your own first. So you get no help from the retailer. For example, Amazon controls all promotion on their site. As an indie with a small to medium sized audience, you are shut out from special promotions that could help you even when they apply. (Like if they are running a Halloween promotion and your book is perfect for Halloween, you won't be included.) It is the old adage of success breeds success.
So at least looking at if from a broader indie perspective, you are pretty much on your own to drive traffic. It takes a lot of continuous effort and creativity.
While I haven't tried app stores yet, the model appears to me to be quite similar to that for books.