Well, you could look at any UI I come up with, then do the exact opposite.
Seriously, I have close to no UI/UX skills. The closest I can come is in terms of API design - that's a style of UX, but very different from web or app design.
To speak (yet again) from ignorance, I would expect that important aspects would be:
- Working out how you're different from your users
- Working out what the most important user experiences are, and making those awesome
- Getting feedback and listening to it