DO NOT list; UX/UI:
Working on web design:

• Do not forget about alignments of the elements on a page; use grid system
• Do not make many focal points (it should be only one)
• Do not forget about visual hierarchy
• Do not make your design busy, without white space
• Do not use clipart under any circumstances
• Do not distort/stretch images
• Do not use low resolution images, unless they are for web
• Do not use too many colors
• Do not use crazy gradients
• Do not put complimentary colors with the same intensity together, especially green and red
• Do not put an image on a background of a similar value unless you have a reason to do it
• Do not break any of the graphic design rules, unless you have several years of experience and know them perfectly
• Do not assume that your design is good until you have a solid experience, always ask an opinion and an advice of a professional.

UX/UI, User friendly website
User friendly website has an interface that is easy to navigate, usable and accessible, looks good, etc.
The main features:
- Consistency - making design coherent between pages and on the same page.: heading sizes, font choices, coloring, button styles, spacing, design elements, illustration styles, photo choices, etc.
- Precedence - guiding the eye (visual hierarchy)
- Navigation - being able to figure out where to go or where you are; should be on the same place on each page.
- Usability - think about user tasks: certain things people need, expect and find without confusion,
- Design itself - alignment, clarity and white space, typography, etc. (read DO NOT list at the left)
And much more

Very good example