I am a huge fan of prototyping. Whether it's creating paper prototypes, something quick and dirty in keynote or invision, prototyping is a great way to express an idea.
These days there are a lot of great tools at our disposal that let us express our ideas and get things out of our heads and on paper.
So really there's no excuse. Here's a few examples of things I've done:
Hierarchy of needs sort:
This is great when working with potential customers to understand their mental model of what they think is important and how they prioritize information and content.
The next thing you can do is create simple motion prototypes in Keynote. Yes Keynote. I've created animations in minutes. This helps you understand the flow of how a customer might move through an application.
And finally there is the more full blown clickable prototype you can create in InVision, Framer or something like UIKit. This is when you want something a user to try out a flow on the front end (without any backend work).