The internet is full of "20 Best Android Apps" reviews, but generally you have to start from your own needs, not what others are installing.
The most common classes of programs are, of course, instant messengers, games, mapping and navigation applications, dictionaries, and taxi calling applications. And then - choose from the app store what you personally need.
I am promoting my blog on Instagram, I want to learn how to cool photo / video editing. There is a lot of information on photo processing, but here's how to work with video ....