Android Development and Getting Started
Java is one of the easiest and most useful languages that exist today. With Java you can make applications for Android, Linux, Windows and Mac. It's an amazing and easy language. Now why Android? For getting into app development Android is the easiest way. You are allowed so much leeway to make what you want, 25$ license to publish on Google Play instead of 99$ just for the software. Android also dominates the world of smart phones, not because it is the best but simply because it is the cheapest (referring to the "30$ Smart Phone").
Lets get into what you should know before you start.
To be brutally honest you need to have patience, sometimes your app will be released and covered by tons just like it, it only takes one holiday to take off(seriously wait until x-mas, your app will take off, generally from all the kids getting phones).
Your app and it's design.
Your app should always appeal to the general user, you need to make it dumb honestly, you can't have an icon and expect people to know what that icon means, text and a tutorial(ShowCaseView), always help the average user figure out the functions in your app. When a user first downloads an app they base your app of the design, I suggest you look into Googles Material Design. The material design looks a lot better (IMO) then some of the other designs people pull out. You can always do your own design but that's a bit more complicated.
Prior Programming Knowledge
You should know your basics of Java before you begin with Android development, sure you don't use a lot of the same methods or classes but the basic syntax and basic method knowledge will still come in handy like textView.setText(), editText.getText(), and many more. If you don't know any Java I suggest taking a course, reading the docs, or fooling around with eclipse or netbeans first and mess with raw Java until you get the hang of it then branch into messing with Android.
Money
The money, this goes for everything related to programming, don't just do it because you want to get rich, do it because you want to program. Do it cause you like to program, you won't ever become as successful as someone who wants/loves to program if you just want money. Now to make the money from Android apps, you usually have adverts on the some of the activities, this will always be a bit of a stain on the design but you have multiple choices for ads when using AdMob you have Banners, and fullscreen ads that can popup at anytime, I and along with many others use banners, they can be tucked away at the bottom of the application out of the way of any useful information. Ad rates vary for everyone. My only app I released that was successful has 80k total downloads and 10k active at all times and I made 300$ in 5 months. It wasn't so bad but of course you have to factor some people spend more time on the app then others. If you had an addictive game/app like iFunny or Flappy Bird you would make a LOT more off of these numbers.
Marketing
When releasing an app, the best way to get downloads and concurrent installs is to market it, how could you market an app? If it is similar to one that already exists simply make it better, make it easier to navigate through the app, easier to understand, faster, and just more appealing in design. If you have a calculator that looks like a 10 year old made it with basic +/- functions or a calculator that looks amazing and flat and gives you addition, subtraction, division and multiplication, which one would you choose? Simply the better looking and better functioning calculator right? I surely would. One good way to market anything is to buy adverts. You can buy them from where ever you please, you can also simply just use tags in your description to get more downloads. If you play with your words just right you will end up having more installs than someone who just plopped there app on the market with nothing else.
Your best friends in development
These are some tools you can use in your journey to develop Android applications.
Stack Overflow(People here are kinda dicks and but they are very smart)
Androids Documentation Pages(Everything you will ever need is in here, the classes, methods, and what they do)
Vogella(Many tutorials on Android Development like their ListView tutorial)
And to get a Google Play Developer
And I am sure some others have some more, feel free to post more useful information/sources below if you have any!
Good luck!
