Here's some searches I just did that seem to be full of great ideas. Many of which I wouldn't have thought of but now I know it took only a few seconds... Imagine how much more informed you'll be if you take a serious approach and spend 10 hours (which is nothing) searching and making notes and taking action. Here's a tip, do at least one thing suggested in every article until you've done 100 things to market your app. Do just 10 things over the next 10 days. That's not much to ask (think about the effort that big companies do to promote and market their apps) and I bet you'll have way more than 50 downloads and you'll have a bunch of feedback as well.
25 Creative Ways to Promote Your App For Free
A Beginner's Guide to Starting and Marketing an App
https://www.apptamin.com/blog/app-marketing-strategy/
https://buildfire.com/free-app-promotion/
Five Killer Marketing And Distribution Strategies For Your App
https://blog.kissmetrics.com/how-to-market-your-mobile-app/
https://blog.kissmetrics.com/11-mobile-app-pitfalls/
8 Ways to Promote Your App
10 New App Marketing Strategies - Apptentive
Infographic: How to Promote an App? Guide to Mobile App Marketing
Top 10 Free Websites to Promote Your Mobile App | MobiLoud
65 Simple Ways To Promote Your Mobile App
How To Promote Your Android App /Game - 10 Awesome Tips
10 Free Ways to Market Your App!
Here Are 18 Ways To Promote Your App For Free | Androidheadlines.com
25 Creative Ways to Promote Your App For Free
A Beginner's Guide to Starting and Marketing an App
https://www.apptamin.com/blog/app-marketing-strategy/
https://buildfire.com/free-app-promotion/
Five Killer Marketing And Distribution Strategies For Your App
https://blog.kissmetrics.com/how-to-market-your-mobile-app/
https://blog.kissmetrics.com/11-mobile-app-pitfalls/
8 Ways to Promote Your App
10 New App Marketing Strategies - Apptentive
Infographic: How to Promote an App? Guide to Mobile App Marketing
Top 10 Free Websites to Promote Your Mobile App | MobiLoud
65 Simple Ways To Promote Your Mobile App
How To Promote Your Android App /Game - 10 Awesome Tips
10 Free Ways to Market Your App!
Here Are 18 Ways To Promote Your App For Free | Androidheadlines.com