1) You don't have to be a good marketer to set up a twitter account and tweet when you add new levels and new features. Retweet them from your personal twitter account and it will at least hit your followers. Don't feel ashamed of asking a few friends to also retweet to their followers. The effect might be small, but it's a minimal effort.
2) Focusing on one app is a bad idea. It's like having a stock portfolio of 1 company. Make several games, even if they're smaller and less polished. You might see that one is more successful and can then concentrate on making it more polished.
3) Most important: do what you love. Don't make your platform, language, or design decisions based on what your google analytics says will make you a few bucks more. If you do that you might as well go back to working secure corporate jobs.