Unlike the popular belief that only SEO and PPC campaigns help increase the conversion rate on a website, I think Website Usability is also an important factor. Both website usability and SEO/SEM are iterative processes, meaning that methodology based on a cyclic process of prototyping, testing, analyzing, and refining a work in progress.
“On the Web, findability is a huge challenge. Can your users find your website? If they do, Can they find their way around your website? And, can they find your products and services despite your website? When you start asking these sorts of questions, it becomes obvious there’s no bright line separating usability, findability, information architecture, and SEO.” said Peter Morville, President of Semantic Studios.

There are various elements that can annoy your users :
1. Illegible Fonts: Small fonts or fonts that don’t match the look of your site.
2. Links & Navigation: The links that have been visited by the user should be displayed in a different color to avoid confusing the user. For sites with a lot of links, navigation becomes easier when the user can distinguish between the visited and the unvisited links.
3.Violating design conventions: Inconsistency is another major issue. All the pages on the site should maintain a flow. The pages should have some sort of consistency and not look like different websites altogether. e.g. the colors of the pages, the positions of certain links like the “sign-out” button etc..
4. Product differentiation & comparison: Emphasize what your site offers that’s of value to users and how your services differ from those of key competitors
5. Make the site’s purpose clear: Include a one-sentence tag line – Include a tag line that explicitly summarizes what the site or company does.
6. Help users find what they need: clear search box
7. Other Errors: Typos, bugs in the script, corrupted data and linkrot(unused links)

At the heart of iterative design is the objective observation of interaction between users and an interface: not focus groups, not web analytics, and not an SEO professional’s personal opinion about website usability.