User validation is not something one do when the product is done developed. User validation can be made in different ways through out the design process. Co-designing with actual user is a great way of letting them be a part of the product. Getting time with the users can sometimes be hard to find. They may have busy jobs or they might be on a whole different location than you are. Setting up some kind of discussion forum where every user can see what is discussed is much valuable. In a recent project we set up a closed Facebook group where we posted design ideas and the users came with direct feedback and ideas. By doing this, we knew that our users were with us. In the end they really longed for the product and they started to tell their friends and colleagues about what was ongoing. It became a great marketing channel.
Some projects require formal user validation in terms of usability testing. These types of tests needs to be planned to get the right users scheduled and to set up the test environment. The tests in the validation must be cohesive so that the user is able to get in a flow. To end the user validation the System Usability Scale (SUS) is a ten-item attitude survey that sums up what the user feels about the product. The SUS scale includes the aspects of effectiveness, efficiency, and the satisfaction of the user.