Working with the user you are designing for is crucial in human-centered design. Testing with users challenges your assumptions about the issue you are solving and can affirm or refute ideas you develop. Users are people with their own lives and obligations, so set clear goals and expectations when recruiting them for interviews or testing. Communicate that you are here to learn from and work with the users to design solutions.
Effective ways to do this include:
At UC Berkeley, an education team focusing on supporting underserved students educational goals utilized a local parents listserv to reach of 30,000 potential users at once. The team crafted a short announcement asking to interview parents and students about their aspirations and goals. The team was able to get a few interviews set up in the following week based off of their post. Utilizing local listservs and forums is a great way to reach a large number of potential users or partners quickly!
Saki, a Leadership Studio participant from UCLA reached out to her Facebook network to recruit users for feedback during Leadership Studio 2015. Many LS 15 participants reached out to their networks and got lots of participants who were interviewed during the weekend!