The Thirds Rule of Thumb

Applied to photography and other visual arts such as painting and design, an image can be divided into nine equal parts by two equally-spaced horizontal lines and two equally-spaced vertical lines ... the four points formed by the intersections of these lines can be used to align features in the image.

David Rogers Rule of Thumb

If it looks right, it's right ... if it don't, it ain't!

Google Rules of Thumb

1. Focus on people - their lives, their work, their dreams.
2. Every millisecond counts.
3. Simplicity is powerful.
4. Engage beginners and attract experts.
5. Dare to innovate.
6. Design for the world.
7. Plan for today's and tomorrow's business.
8. Delight the eye without distracting the mind.
9. Be worthy of people's trust.
10. Add a human touch.

[Sue Factor, User Experience Group, Google ... Thank you, Joe Driear]