Sort of a Maslovian hierarchy. I.e. don’t attempt a subsequent step until you get the previous step right.

  1. Load fast
  2. Don’t break the browser or the web (e.g. bookmark-ability, back/foward, searchability, etc.)
  3. Align with core web UI conventions (e.g. use hyperlinks for navigation, use forms for data entry)
  4. Be consistent with other web apps in your product family if you have one (e.g. all Google apps, all IBM apps)
  5. Make it pretty and do cool stuff if if it helps your users be more productive and/or have a more pleasant user experience