I make Android apps for a living. Torn between the guilt of giving away free advice and the guilt of seeing people need help, so I'll try to strike a middle ground. I'll just go for the common sense stuff that you can maybe pick up from Google
Mobile marketing is entirely different to say, PC marketing.
People aren't going to find your apps on Facebook or whatever. They'll learn about it almost fully through browsing or word of mouth. Similar with review sites. Review sites do work for hardcore gamers, but often it's easier to just search for it. However, people will sometimes look up your game on a review site before buying.. low prices will encourage impulse buying.
Trailers are excellent. Don't bother with putting captions on your screenshots, it just makes it look like you're hiding the actual gameplay.
Hit the right keywords. Ranking does NOT equate to sales. It does equate to more views, though. Great for casual stuff that appeals to everyone.
The people who search for your keywords are often the people who want to buy that kind of stuff and the people who would pay a premium for it. Like, I normally search for "roguelike". Someone may search for "platformer" or "strategy" or "angry birds" (as a genre). Make it clear what your game is.
Don't be an idiot and spam those things everywhere, though. Dunno about itunes, but Google's recent algorithms are designed to punish SEO. Be honest, don't game the system too much. Experienced gamers don't like marketers and if you're going to appeal to casual/dumb gamers, just make a pay-to-win.
Mobile is basically about getting as much information to the user in as few words and pictures as possible. Information is distilled into one small page, get to the fricking point.
If you're indie, doing it with a tiny team, marketing is just really poor return. Just google a little over a week or so, and spend the rest of your time making something good. It pays.