When I start a design project, the process that I follow is described by the Nielsen Norman Group in their Design Thinking 101 article.
It is a user-centered process that starts with user data, creates design artifacts that address real and not imaginary user needs, and then tests those artifacts with real users.
This process consists of 3 flows:
understand explore materialize
Further defined by 6 phases:
Conduct research in order to develop an understanding of your users.
Combine all your research and observe where your users’ problems exist.
Generate a range of crazy, creative ideas.
Build real, tactile representations for a subset of your ideas.
Return to your users for feedback.
Put the vision into effect.
One important takeaway from this process is that it encourages flexibility and iteration through the phases, repeating as needed. It is not a rigid set of steps to follow.