I started by participating Massive Open Online Courses (MOOC) Object Oriented Programming with Java, parts 1 & 2, organized by Helsinki University. Then I installed Android Studio to my laptop, paid 35$ to Google and started to develop my firts Android application called "Event Costs Splitter". It took me approximately one year from first theory session to app release. It is a long time for small project, although I did coding mainly while my most important "project" was having her nap. And yes, your firt app will be donwload only five times as pointed out earlier. And yes, my ultimate goal to get my money back from Google is still very faraway. Still I think it was time well spend. In fact, I have two new ideas on my head already.
Your question was how to make money with your app? I believe it depends how your app will be used. If you app is really usefull, but really needed, sell license. If it is "allways on top", use adds. If it is addictive, use subscription. If it makes users life easier, collect fees.
Try to answer also these questions. How much money you have spend on apps? Why? What annoys you on apps? Why? Who has money on the pocket and is willing to use it? On what?
Conclusion: Go for it! If you don't try, you don't have chance to succeed. You will hear sentence "Ain't that kind of app already exists?" many times, don't let it stop you.