We have a look at Gould and Lewis’ 1985 paper ‘Designing for Usability’  in which the authors present and discuss three principles for user centered design:
- Early focus on users
- Empirical measurement using prototypes
- Iterative design
Goult and Lewis explicitly differentiate between understanding potential users, versus identifying/describing/stereotyping/ascertaining them. They also strike a crucial cord regarding the neccesity to separate the role of designers and developers for a simple reason: It is cognitively impossible for developers (and other stakeholders) to pretend to be a novice user. I wrote a separate blog post that proves this to you with an amusing example.
Gould and Lewis recommend that potential users become part of the design team from the very outset. Next to that, they emphasize the importance of iteration, a process that enables cycles of designing > testing > measuring > redesigning >. Wallach and Scholz  describe a more contemporary cycle of design activities, consisting of Scope > Analyse > Design > Validate > Deliver.