Today I was on an app called "FeaturePoints" which I like to occasionally go on in my free time. It's a great app that lets people accumulate points by downloading apps and using them for a certain amount of time. With the points you gain you can purchase things. But the good things about this is that FeaturePoints is acting as an advertisement for other apps. And there are many other apps like FeaturePoints that do this promotional things. This is only one app marketing strategy. There is also software like AdMob which helps advertise your app in other apps, like a banner or short clip. The best and most efficient way to promote/advertise your app is to showcase it on a micro-site (a one or two page showcase about your app). Also, another good way to promote is a video, which is what Pascal is making. The video is a prominent solution to advertising because you can add it to any media site like (YouTube, Vimeo, etc). Another way to promote you app is through a podcast/radio but those are not extremely robust because it's not likely to attract a large group of audience.
Source (more promotional ideas): http://www.entrepreneur.com/article/229305
Source (more promotional ideas): http://www.entrepreneur.com/article/229305