How to promote the app in play store?
These are the 3 thing you can do to promote your app.
- Post in App Review Submission Sites
- Write Articles about your app through guest blogging
- Press Release writing for your app
Hope it helps 
You have to advertise it. I recommending you Google or Facebook option, using worldwide targeting (helps to keep the cost low).
Beside of these, run incent traffic, like: high retention installs (7 days).
Register and you can create a campaign within few minutes: https://androidinstalls.com
At first develop really valuable app, where you include really quality design and features which are in demand by average user.
Then publish your App in Google Store. Before launching your App in store care about[b] optimization your app[/b] (it means - you need to conduct decent keyword improvement and care about putting it into title and description). It really helpful procedure which will generate a lot of organic audience which searching your kind of app in search line.
At every beginning of publishing start the installs campaign. Installs are key factors in Google App promotion. They will allow n you to improve position, be visible and reach the target audience. The installs can be ordered in reputable company which are specialized in inner Store promotion. As an example – recommended one is KeenMobiwhich propose a wide range of service for marketing your app in Store: ASO, positive reviews and installs.
Start your promotion right now and do not miss the opportunity to get benefits from well-promoted App!