Sometimes, it dawns on you that the basic principles of a particular field are either not known or not established.l. I firmly believe this is the case with UI design. I've been an end user for decades, a software trainer from time to time too, and am presently working on a UI for a form with well over 100 input fields. I'd like to put forward the following as fundamentals:
1. An interface should be intuitive. That means that someone who has never used it before can do so. Measure the success of your UI by the number of times that a new user is halted by their lack of previous knowledge. How often do you 'just have to know' where something is located in order to be able to use it straightaway? When a user doesn't know, how long does it take for them to find it? Measure that. Test it.
2. I don't believe that users are best served by a tailorable interface. If an interface varies according to set ups and preferences it soon becomes impossible for users to be given simple advice on how to use it. With an unvarying interace, support from co-workers will be more prevalent. Long and complex explanations soon destroy the users confidence ("How come such a simple thing is so complicated?") in both their abilities to use the software and the ability of those teaching them ("Ah... now that doesn't work because... hmm... let me see... maybe you've got...").
3. For tasks that end users use a lot, UI designers should flow chart the minute processes that a user will go through to achieve the task. As long ago as Apple's System 7 it had become very easy to organise files, navigate directories and find anything. That's now a much tougher process in almost all modern OS.
4. If there is always going to be at least some learning for an end user to do, produce a simple and learnable system rather than a complex one that tries to compensate for the failings of the lowest 10%.
5. Keyboard shortcuts? Handy if it is quick to find out what they are. Not handy if you need to pick up a manual or google for twenty minutes. Show them alongside their equivalent menu commands and everybody's happy.
And if you think I might only believe the above because I'm too dumb to use a computer, be assured that I have done more than enough to prove otherwise. Really.

One thing above all: Time spent learning a new system is unproductive, and people aren't silly for being averse to that. Aircraft designers used to have a saying, 'Give me enough power and I'll fly a barn door' . The equivalent for UI designers is asking users to spend time learning their product. Ask too much and there's a chance your product isn't worth the time that has to be lost in learning how to use it.