Sketching is a magical method. It's easy to believe that just putting your ideas down on paper won't lead to more ideas, but it often does, and that feels magical. It's also very simple. Take a piece of paper or digital equivalent, and start drawing out the first idea you have, then the next, and so on.
In The User Experience Team of One, Leah Buley explains why sketching is useful:
In user experience design, there are usually a variety of directions a design could take. Sketching is a thinking tool that you can use to pinpoint an idea and then adjust and adjust again. It can also be used to generate a range of potential solutions to a particular problem. This makes sketching an excellent tool for exploring constraints and trade-offs, and thinking through the implications of one design over another.
If you sketch an idea on paper, it literally gets the idea out of your head and in front of you so that you can consider it more objectively. Things you assumed would work in your head suddenly don't when you're forced to draw them. But more importantly, seeing an idea in front of you will spark other ideas that build off the first one. For whatever reason, it's not as easy to build ideas on top of one another in our heads.
Annie needs to design a mobile screen where someone can choose multiple items and carry out an action on all of them at once. She knows it might be a tricky interaction design challenge, so she decides to sketch her ideas as they come to her.
She takes a piece of paper and draws an outline that's roughly the size of a mobile screen. She starts drawing the items in a list and gives each one a checkbox. At the bottom of a list she puts the action that the user will take on all of the items.
She realises while she looks at the sketch that if the list gets longer, the action won't be visible on the screen any more, and users might not know what the checkboxes are for, not to mention that they take up precious space.
She sketches a new idea, where the user switches to a "selection" mode, and the action they take on the items is always visible on the screen, floating above the list. She likes this idea, and so does her manager, so she works with a developer to prototype it.