Guidelines for Usability Designers

Few questions which needs to be answered before designing the User Interface for an application are:
1) Who are the users? Their age group? Their Specific Location (if any)?
2) Will user be trained before they will use the application?
3) How much automated task should be provided and how much left for the user?
4) Will the application be shown on other gadgets like PDA and Mobile? 5) How much compatible it should be.
5) Will the machines needs to be remembered few tasks?

Few things which should be included:
1) Ease of Navigation
2) Consistency need to be followed
3) Help Section
4) Error messages should be specific
5) Helpline Number to solve the query quickly.
6) Standard look of icons and an option to show Icon and Text together.
7) Search functionality
8) Differentiate links from normal text (best would be to underline it)

After designing the application few stuff which needs to be checked are:
1) Can user really be able to complete task?
2) How easy it was?
3) Do they require more training and support files?
4) Keep testing

Let me know if i have missed anything.