Jakob Nielsen, Ph.D., is a retired principal and co-founder (with Dr. Donald A. Norman) of the Nielsen Norman Group. Jakob established the "discount usability engineering" movement for fast and cheap improvements of user interfaces and invented the heuristic evaluation method.
Users visit websites and use apps to get things done, so emphasize the content of interest to communicate with your audience. Avoid design pollution that decorates the UI with noncommunicative elements.
Some UX designers (and many clients) aim to "jazz up" the design to supposedly engage users. This usually backfires because extraneous design elements get in the way of users' tasks.
Among high-legibility fonts, a study found 35% difference in reading speeds between the best and the worst. People read 11% slower for every 20 years they age.
The road to usability is paved with temptations to complicate the design with extra features and options, but resisting featuritis is the best prescription for a good user experience.
The foundation of user experience is the difference between the people on the design team and the people using the product. You can't ask users to design, but you also can't ask the designers whether their own design will be easy for the target audience to use.
The best way to learn UX is by *doing* UX. Knowing some theory and concepts is key, but superior skills are built by reflecting upon the outcome of practicing the skill.
The computer mouse is the most efficient pointing device for speed and accuracy. More important, it's the symbol of user empowerment and control over the user interface.