Jakob Nielsen's 10 general principles for interaction design. They are called "heuristics" because they are broad rules of thumb and not specific usability guidelines.
Usability
10 Usability Heuristics for User Interface Design
Knowledge
How To Write Email Newsletters That People Actually Want To Read
Affinity diagramming has long been used in business to organize large sets of ideas into clusters. In UX, the method is used to organize research findings or to sort design ideas in ideation workshops.
Workshops
Affinity Diagram — NN/g
Knowledge
The Business Marketing Pyramid That'll Make Freelance Clients Come to You