Confusingly similar links

Examples: “About Us” and “Our Story” on the same site; or “Customer Login” and “Secure Client Area” on the same site. Which is the link I want?

Confused or non-existent hierarchy of reading

The classic example here is the “everything is equally important” syndrome. A website suffering this is filled with links and heading and pictures all roughly the same prominence, or all flashing wildly for attention.
Unnecessary animations and adverts can also get in the way of usability and communication effectiveness. Careful treatment is required to appropriately isolate these elements from the rest of the site.

Inappropriate copywriting

People tend to scan text online more so than they do on paper. Your copywriting needs to accommodate this. Generally, stick to one concept per sentence, and one theme per paragraph. Keep it short. Use headings.

Insufficient signposting

Effective signposting helps users navigate your site and create a coherent mental map of your messages. Effective signposting depends on a sound underlying architecture – strategic planning is required.
Ad-hoc organic growth can be dangerous, especially for content-heavy sites.

Interference from Search Engine Optimisation (SEO) practices

Some SEO practices can inadvertently cause confusion for mere humans. Examples: creating loads of similar looking “landing” pages with minor variations; and adding excessive and unnecessarily content to pages.

Targeting the wrong audience

Example: the painfully repetitive over-the-top animated splash page that was designed to stroke the CEO’s ego (who only looks at the site twice a year). Reality: customers just want to get into the site and buy something.

Example: the super-prominent link to the minister’s message, with a big photo, on a government website. Reality: the public don’t give a poop about the minister’s (unchanging) message and just wants the info on the site.