Its very hard unless you get lucky to make money with your android games and apps. The road to building a decent income is long and hard but can be done. Here are some minimum requirements if you don't want to let luck determine what your going to make money off of. It might seem like a lot of work but marketing is really the only way to accomplish earning a decent income off of apps and helps with the luck factor.
Minimum Marketing Requirements
1) Post in various app stores that have good traffic. Besides Googleplay there are other stores that have good traffic and promotional deals. Appstores such as Slideme , Samsung and Amazon all have decent traffic .
(Now only Amazon has decent traffic the others not as much )
2) Post in many different Android forums such as xda-developers,making money with android and androidpitt. Even though this might not get you a ton of downloads most appstores place apps higher on charts that have a good amount of link backs to the app page. This is the missing link in ASO that developers forgot.
3) Post on social media like facebook ,instagram and twitter. Posting in these places will only get you a few download but its helps with the LUCK factor. Social Media is mainly the way most games and apps go VIRAL.
4) Art- not a marketing strategy per say but high quality artwork in your games , apps and most importantly your icon will draw in much more users to your app.
5) Youtube video's - Having a youtube video so users caan see the functionality of your games and apps is a free way of getting more users to your game or app. Also youtube is a gateway to help your game or app go VIRAL especially if the artwork is high quality.
There are more ways to market and promote your games and apps but this is a list of basic marketing you must do in order to make money with android.