I have this linked in another post, but it’s certainly worth its own explicit posting for folks to link to for future reference:
Dieter Rams 10 Principles of Good Design
Good design is innovative.
Good design makes a product useful.
Good design is aesthetic.
Good design helps us to understand a product.
Good design is unobtrusive.
Good design is honest.
Good design is durable.
Good design is consequent to the last detail.
Good design is concerned with the environment.
Good design is as little design as possible.
Back to purity, back to simplicity.