27 Usability & Web Design Guidelines according to "strength of evidence"

HHS and GSA had done a comprehensive research to generate a list of usability and web design guidelines.

1 Use an Iterative Design Approach
2 Provide Useful Content
3 Use Black Text on Plain, High-Contrast Backgrounds
4 Ensure Visual Consistency
5 Standardize Task Sequences
6 Use at Least 12-Point Font
7 Use Video, Animation, and Audio Meaningfully
8 Order Elements to Maximize User Performance
9 Use Mixed Case with Prose
10 Facilitate Scanning

11 Group Related Elements
12 Design For Working Memory Limitations
13 Ensure that Images Do Not Slow Downloads
14 Use Descriptive Headings Liberally
15 Recognize Tester Bias
16 Emphasize Importance
17 Design Quantitative Content for Quick Understanding
18 Use Familiar Fonts
19 Use Simple Background Images
20 Align Items on a Page

21 Use Color for Grouping
22 Choose Appropriate Line Lengths
23 Use Attention-Attracting Features when Appropriate
24 Use Heuristics Cautiously
25 Use Cognitive Walkthroughs Cautiously
26 Use Data Entry Fields to Speed Performance
27 Use Images to Facilitate Learning

The above are 27 important usability and web design guidelines based on maximum score of 5 (on rating of 1 to 5) for “strength of evidence.” These are obtained from Research-Based Web Design & Usability Guidelines.