This, of course, is 100% true. Designing a mobile app or a website may sound easy, but in reality, it is fairly difficult. In my experience, while working with mobile app developers, the hardest part is 'finding an appropriate design for an app'. The app's interface must be relevant to the type of app that you are developing.
When it comes to brainstorming your app's design, I always look for inspiration on Pinterest.
Some of the major app development companies can be found on Pinterest. Furthermore, just by scrolling through some app design ideas, you can come up with something creative and unique.
How I do it?
It's really easy. I just type in some keywords relevant to the type of app I want to design, and voila.
-Health app design
-Kids app design
Where do you look for inspiration for designing your apps?