Can you provide some examples of apps that have a great onboarding user experience? One where they walk a random visitor through signing up and setting up aspects of the account, etc.
Pinterest is one. They have clearly spent a lot of time polishing up their onboarding.
What are some elements that you should pay attention to when creating your own onboarding UI?
I was recently impressed with Slack.com. They have a chat style Q&A to gather your profile information. It was seriously the most fun way to fill out my profile.
I also liked Canva's onboarding. It walks you through the essentials of creating a design. They take something that could be difficult to figure out and simplify it. It's better if you actually experience it but if you want to glance at some screenshots, you can download them here.
Udemy has a course that takes you through different onboarding techniques. I wouldn't say it's worth the $249 listed there but I got it for a crazy discount at the time. You may also want to check out this User Onboarding site's teardowns.
UX Archive has some of the best mobile app onboarding teardowns.
Usually mobile apps have to make their processes simpler than full desktop apps. So it would make sense to create your onboarding process for the mobile first, and then just adapt the design for larger screens. This way you'll limit the steps and keep it simple.
Checkout this post on Betterment as well.