Sketching can be a extremely quick way to make roughs and communicate with the user. The user can then be exposed to the ideas and make low-fidelity tests. New prototypes can be generates and new ideas tried out.
Try to sketch a quick prototype of an app for a phone, which can help people fix their bicycle or another purposes of your choice. Test this with a user, think aloud-test and make notes. Revise the prototype and try again.