Know thy user
Is it science . . . some other drama perhaps?
User Research, Requirements, Journey Mapping, Experience Flow, Wireframes, Interactive Prototyping
...testing assumptions by getting out of the office and having conversations.
I can think of no other way to understand anything meaningful or of any relevance to any problem needing solved for the collective we call humanity than listening, no matter what role you play in the development of useful and used apps.
...co-planning between design and development teams with focus on back & front-end compatibility
Thoughtfully designed prototypes, iteratively executed through ongoing discovery processes around user and use scenarios