User-centred Design
It is essential that designers have a strong understanding of their target demographic (the people they are aiming for) so that they can better meet their needs. This page will help you consider how to do this. In an age where it is so important to avoid discrimination, it is important that we also consider our user's gender, religion and beliefs as well as if they have any additional needs due to things like disability.
Everyone has a right to be treated the same and should not feel excluded from using a product or carrying out a task.