Take a close look at Inside Macintosh. Volume 1 if memory serves. One thing I do recall is that a menu should be +/- 7 menu items. The reasoning is that people

Take a close look at Inside Macintosh. Volume 1 if memory serves. One thing I do recall is that a menu should be +/- 7 menu items. The reasoning is that people can remember about seven things. Default buttons (ok/cancel) should always be non-destructive. You don’t want your default button to delete a file, for instance. The reasoning is that users will hit return by default on a dialog box. The most important thing I’ve learnt over the years is workflow. Build your UI by having actual users use it and critique it. As an example, if you’re filling a form or table in, move to the next cell/field when they hit tab or return. That’s one thing that makes an application good versus useable.