Intuit recently published their style system called Harmony 101. Apart from a styleguide and a pattern library it also consists of these design principles to guide the way Intuit's software is designed.

1. Establish a familial resemb­lan­ce. Drive consis­tency and integr­ation in the experience to keep the journey seamless, familiar, and harmon­ious.
2. Maintain user context by staying in place. Prioritize in-line or modal viewing and editing over new views or contex­t-s­wit­ching.
3. Guide the user where approp­ria­te. Help users understand what to expect through progress charting and First Time Use tips. Provide useful views that guide toward common tasks.

1. Be trustw­orthy and helpful. Auto-fill commonly requested inform­ation for the customer and provide insights to help users improve their business financ­ials.
2 .Imbue confid­ence. Avoid re-inv­enting the wheel; rely on familiar conven­tions when introd­ucing users to new tasks. Don’t leave the user hanging; provide dynamic feedback where possible.

1. Define a standard person­ali­ty. Apply consis­tently across the Harmony suite of apps to provide unity and cohesion.
2. Celebrate unique tasks. Create ownable intera­ctions and visual expres­sions that are a familial extension of the design language.
3. Project a voice. Define consistent use of voice to inject fun into the user experi­ence.
4. Define ownable visual­iza­tio­ns. Use visual­iza­tions to compliment data, channel person­ality and provide stickiness in the experi­ence.

Cele­brate data while respecting user & device context
1. Be smart and approp­riate for the task at hand. Use progre­ssive disclosure of data and inform­ation, provide real-time feedback, and simplify required steps in task flows.
2. Understand the broader contexts of use. Minimize chrome and embell­ish­ments; design for user custom­ization and person­ali­zation where approp­riate.