QA is critical. The user’s experience has to feel smooth for them to keep using your app.
To QA your app, start with devices. Get four phones: one modern iPhone, one modern Android, and two older models, one iPhone and one Android.
Buy them secondhand on Facebook Marketplace. Remember, most users will not have a high end phone.
Set up Sentry and connect it to Slack so you get notified when the server goes down. This is a must. Sentry is the industry standard.
Stress test the app. Push it as much as possible. Simulate 3G and 4G connections, since most people do not have reliable WiFi.
Add tests and benchmarks to both the front end and back end. If something takes more than a second to load, it is not optimized.
Before launching anything, ask yourself: is this the simplest way to do it? Even a single extra tap on the screen is friction.
For example, if you want users to play a video, do not make them tap. Let it start automatically. Why do you think TikTok plays videos automatically?
Always reduce friction. Do not make them think.