Example Site Usability Audit - (click the images below to see the report pages)

Accessibility: It is necessary to ensure users can accessibly navigate sites easily and extract the relevant information.The World Wide Web Consortium's (W3C) leads guidance for promoting a high degree web site accessibility. Royal National Institute of the Blind (RNIB) is an active member of the W3C, and most of their guidance is based on the Web Accessibility Initiative (WAI), recommendations. The Disability Discrimination Act 1995 makes it unlawful to discriminate against disabled people in matters such as recruitment and employment, the provision of services and the provision of education. The Disability Rights Commission is an independent body established by Act of Parliament in April 2000 to stop discrimination and promote equality of opportunity for the 9.8 million disabled people in Britain. It supports disabled people in getting their rights under the Disability Discrimination Act.
Where non-text elements are used, the same information should be provided in a textual format, to enable all users to access it. For example - an option available to people with sight problems is to use a speech browser or a screen reader. This software will read out, in a synthesised voice via the sound system on the PC, the contents of a web page. Graphic images are obviously not directly accessible to this kind of software, but the addition of a text alternative through the use of the ALT attribute provides text which can be accessed by speech browsers, screen readers and text-only browsers. The addition of meaningful alt text to images is one of the most basic techniques for making the content of a web page accessible to a wider range of users. Modern accessible design techniques, for example use HTML DIV tags and Cascading Style Sheets (CSS) rather than HTML tables to achieve positioning.

Search Engine Marketing (SEM)
Most of the spend on the Internet is on search engine marketing.

Search Engine - Pay Per Click (PPC)
This is when companies pay to advertise their site on search engines such as Google or Overature.
Important points to note are that the amount paid for the keyword or phase(s) selected is optimised. Most of the larger SEM companies have a Bid management function which monitors what the next lowest price is. Therefore it's not always the best strategy to say "Oh yes, we want to be at the top of the list". Well, you can but you can also pay over and above for it.
Watch your copy, change it and keep things current.

Search Engine Optimisation (SEO)
A well ranked site, brings in traffic at zero cost. This is called natural rankings or organic optimisation.