Practice a lot
One of the best tactics that helped me at some point was to pick a not-so-great app from the App Store, one of those with poor visuals and UX. Then:
How to Practice
- Identify 1-2 major scenarios users are supposed to accomplish within the app (I would advise not more than 5 screens for each scenario; keep it simple for starters)
- Identify one business goal (ex., increase subscriptions).
- Find a few references: one for UI components, one for layout, one for colors, one for typography, and one for graphics.
- Then, having it all, get to work redesigning it.
- Create a prototype in Figma and test it yourself, with friends, parents, anyone.
- And then iterate based on your findings.
The major difference with the real world here is that you would complete the same steps but just on a higher level with real business problem, data, and feedback and have more collaborators in your team.
With each redesign, you'll be mastering your mobile design skills bit by bit.
Practice really does make perfect!