There are a lot of things to learn while you are developing the android application. 
1. For the beginner it is also more difficult because there is very few or low content available in the open market for learner. 
2. Many a beginning developer start learning from YouTube's channels but don't practices properly. That is why fails to learn the basic thing properly.
3. A lots of updated framework are developing day by day so become confused what to learn and starts scattered learning it is very bad and will ruin you.
4. Start learning from the basic that will help you and start practicing
5. Learn the android sdk well so that each of its functionality are atleast know to you. 
6. Then start practicing, make a copy of your own app before starting it for your client . 

Thanks that's it 

If you like you can check my running App from play store build for an NGO

https://play.google.com/store/apps/details?id=naba.diganta

Android Applications Development Challenges

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