Do you realize that a good interface should not require instructions?

The corner stone of good user interface design is that if your users need instructions, you haven't done a good job. Of course with particularly complex applications there will be exceptions to this rule, but all developers should aim to make your interface as self-evident as possible.

• There are no surprises
• There is no need to use help
• No excuse for RTFM (read the freaking manual)

A good UI is:

• Intuitive
• Feels fast e.g. no white screen, threading code
• Consistent
• Minimal popups
• No clutter - not busy
• Good error handling
• Easy to customize + apps (aka a platform)
• Gamification e.g. badges

Suggested reading:

• The Design of Everyday Things: Revised and Expanded Edition (Nov 2013)
• Don’t Make Me Think, Revisited (3rd Edition)