Every first-time developer inevitably asks you same question. Luckily for you it has been answered many times (you can check my website/blog).
There are many "things" you can do, odds are you should be doing anything you can to promote your app. However, as I imagine budget and time might be limited, you need to prioritize based on target demographic and type of app.
Without having further details, you should definitely try Facebook (to narrow down your target demographic), and push on ASO (to see what keywords trigger your downloads).
As a second step, find online communities reflecting your findings.
third, I'd push with more structured user acquisition platforms which will take care of finding the best balances.
For more information, feel free to reach out to me.