Caroline Jarrett has written a great piece over on the UX Matters site: http://www.uxmatters.com/mt/archives/2012/05/7-basic-best-practices-for-buttons.php
For those of you with short attention spans here is Caroline’s own summary:
- Make buttons look like buttons.
- Put buttons where users can find them.
- Make the most important button look like it’s the most important one.
- Put buttons in a sensible order.
- Label buttons with what they do.
- If users don’t want to do something, don’t have a button for it.
- Make it harder to find destructive buttons.