These are the top 10 Mistakes in Web Design,

  • Bad Search
  • PDF Files for Online Reading
  • Not Changing the Color of Visited Links
  • Non-Scannable Text
  • Fixed Font Size
  • Page Titles With Low Search Engine Visibility
  • Anything That Looks Like an Advertisement
  • Violating Design Conventions
  • Opening New Browser Windows
  • Not Answering Users’ Questions

You can read more about this from here

Cheers………..!