ASO is important but Google play only lists the top 250 results.
Promote your app on Reddit.
Promote your app on forums like AndroidCentral, XDA developers forum, etc.
Answer the relevant questions to the app you made on Quora.
Join groups on Facebook share your app there.
Promote app on Twitter, Pinterest, Google+ community.
create a very nice app promotion video and send it to each and every channel.
Doing all these will surely increase your downloads and your app will be featured in the top list of google play searches. This is what all other people are doing but you need to give continuous efforts for some months.
So Start doing this and let me know if you need any help.
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