A design is only as good as how well the users understand it, enjoy it, and find that it helps them be successful. The Validate phase of design is absolutely crucial to achieving these goals. Below is a sampling of the sorts of key activities that I have done in this area.
Moderated Usability Tests
The bread and butter of usability research is the usability test. Placing users in front of the product, and having them attempt to accomplish certain scenarios reveals so many things.
Unmoderated Usability Testing
Using a bit of game theory, we were able to get a large quantity of users through an unmoderated test at a large conference. Our team took an old video game cabinet and converted it into a mobile usability testing lab. By having the activity timed and a leader board displayed, users were encouraged to come and attempt to achieve the fastest time (prizes were awarded). The goal was to understand the shortcuts they took to accomplish certain tasks.
Card Sorts and Interviews
Not all activities involve the UI or prototypes. Sometimes in order to get a better sense of how to begin crafting a useful product, you need to understand better how the user thinks, or worries and concerns they have.