A design system is a complete set of standards intended to manage design at scale, while a style guide is a piece of documentation that provides specific style guidance.
Understanding and sharing the needs and motivations of users will lead to better design decisions. Observational research should be nonjudgmental while keeping an open mind and reducing bias.
The words in your interface can help establish your product’s personality. The tone of any piece of content can be analyzed along 4 dimensions: humor, formality, respectfulness, and enthusiasm.