"Fred Wilson and the ten golden principles of successful Apps"
This is two years old already but like so much of Fred Wilson it's almost timeless and very ahead of it's time. It is just as applicable to mobile apps as it is to web apps. Great watch.
Here are his 10 points if you are short on time (but really, watch the video!)
1. Speed. Every click delay counts/costs.
2. Instand utility, instant result.
3. A Voice (personality).
4. LESS is MORE!
5. Programmable (read/write API)
6. Personal. (community, having people care about your App)
7. RESTful (not just the software architecture but readable URL linkage for everything)
8. Discoverable (SEO, ground up discovered by Google AND social media)
9. Clean (UI, simple, inviting)