Keep your code clean and semantic while using the latest Web Standards.
Make it Fly
Leave the smallest footprint. Your users don't want to be kept waiting.
Squash the Bugs
This is just a given. Test, Test, Test, and even more testing before a release.
Make it easy to use. Frustrated users who leave, likely won't come back.
Create something amazing that will just wow your users.
Always keep responsive design and graceful degradation in mind.