Most often design principles are associated with really big name designers. For many, principles are whatever the client wants. Principles and clients needs should be one in the same, in that we are both trying to create the best product possible. Often times that product may not even be what was originally intended. This is one of the hardest things about design. After all the research, thought, sketches and prototypes how do you go back to the client and say this is actually what will solve your problem. I have to say that much of my own design principles were inspired by those of Dieter Rams, though I think they stand on their own. Developing your own design principles even as an exercise can be extremely useful and it points out where in your own work you may have compromised without knowing it. So, here are my design principles.
Design is Honest: Honesty is materials, honesty in function, honesty in value.
Design is Respectful: Habits of users should be noticed and accounted for.
Design is Purpose: There should always be a reason for the product to exist.
Design is Simplicity: Simplicity in components, simplicity in use.
Design is Inevitable: The conclusion should seem so obvious in retrospect.