Hello,
I have built apps that doesn't have millions of install but great app enough to impress peoples. I've built a complex cricket app that displays score, analysis and statistics along with schedules, historical matches and all. It has approx 30+ screens and much larger data to handle. App is now somewhat unresponsive since last release, a kind of bug persist in my app which is hard to track down and my developers are not able to find, but you can check that app. It has approx 400k installation. i also have an iOS app that was marvel when I released and It was paid app but like 40k people purchased it and it's awesome.
Now design part, I do carefully research competition, usage patterns, top performing app, user psyche, demographics, languages and key offerings from app and based on that, I create multiple wire-frames that can be essential to understand user flow. Once I get clear idea with your team about required steps are viable and should be taken to next level, I'll start designing with high-fidelity pixel perfect designs that offers experience of real-time usage with flair of animation and other elements. Once we get past wireframes and basic screens. I'll create modular designs that can be applied for further advancement of project like single click will change entire app's colors / elements property and typography.
There's much more to share about my design standards, if you can ping me. I'd be explaining how my skill-sets can add wow-factor to your app. Chat!!!