Developing a game these days can be highly competitive, but if there were ever a place where developers have a great chance at reaching a larger group of people with their game it's on mobile, especially with Android being a booming mobile gaming platform with millions and millions of users. There are many different steps to ensuring you create a successful game that players will love, but one of the most important steps will be the decision on how to monetize your game. You can do this a number of different ways, like an outright one-time purchase, in-app purchases for things like in-game currency, or even ads. Then there are varying levels of each of those models, and of course there are more ways to monetize your app then just choosing a payment model. You'll also want to consider having your app reviewed. Plenty of sites offer an app review service which can be just the traction a game might need.
At some point in the development process, you're going to need to look at the different options for monetization models, and there are many different paths you can take. No one model is right for everyone, which is why it's important to weigh out your options against the type of game you're creating. It might not seem like it, but the target audience, your game type/genre and how you engage players to keep playing can all be factors in choosing the right monetization model, whether that model be a one-time paid game, a freemium offering with IAP's, or a simple free game with ads injected into it.
If you choose to utilize IAP's, there are a few different ways to implement this system, like paying for additional game content such as extra levels. For example, look at the way Telltale Games implements new episodes for their episodic series titles such as Game of Thrones, The Wolf Among Us, Tales From The Borderlands etc. All of these games are set at a price of $5 initially (sometimes cheaper or even free during sales or deals) for the first episode in the series, and then gamers can choose to continue playing by purchasing new episodes as they're released, or pick everything up with a season pass which usually saves them a few bucks. This is one way to implement the in-app purchases, but you can also deploy the use of purchases for in-game items that will enhance the content or give gamers extras at a faster rate then simply playing. Look at Gameloft's Dungeon Hunter 5 as a good example here, which gives players the option to play the game to acquire things like gems, health pots and other items, but players also have the choice to pay for those things with real money.
While many gamers may be put off to the idea of IAP's, there are probably just as many gamers that will not mind them being used and, if they feel the game is enjoyable enough they may even find value in paying for extra in-game content or items. While monetization is important and planning out how you monetize your app is a step that needs to be taken into consideration probably early on, no monetization will be successful if you don't have a game that people think is worth their time. With that being said, make sure you're developing something that people will enjoy playing. Past that, try to drum up some excitement about it that could help people enjoy it more, like contests and rewards for weekly events, rewards for returning every day etc. This kind of engagement can help to keep people interested and possibly make the game more fun.