Firstly and most importantly you should design and build your website with Web Standards at the fore. Amongst other things this will reduce download times, improve search engine rankings, and future proof your content.
Whilst you want to have a visually appealing site, keep it simple. Most users are not design junkies and just want to find information or buy a product. Focus on a strong navigation and graphical elements that highlight the most important parts of the site.
A search is a simple means of quickly improving the usability of your site. Within seconds of arriving at your site users can find information that may be buried deep within your site. Providing an advanced search interface also allows users to perform more detailed searches. Put the search in a prominent position on your site either in the header or near to it.
Showing users where they are in the structure of the site is a simple way to allow users to navigate. A breadcrumb trail usually appears at the top of the page about the main content and tells users which section of the site they are in.
The Information Architecture, or Sitemap is an integral part of a successful website. Construct a broad and shallow Sitemap and try to keep things to three levels if at all possible. Think about what your users want and build the Sitemap accordingly. You can test your assumptions by showing friends or colleagues your primary navigation and asking where they would expect to find things.
Icons are a great way of providing visual cues to specific tasks or features on the site. You can purchase icons cheaply or make them yourself using Photoshop or Illustrator. Keep icons small and quickly recognisable. Be obvious - if you are making an icon for a search use visual language that is quickly associated with searching.
Typically your user base will be performing two or three tasks on your site. This might be searching for information, buying products or engaging in a discussion. If there is one thing that users do over and over again put it on the Home Page in big letters. There is no shame in being obvious if it helps users to get what they want more quickly.
Assume that your users are not sophisticated or technology-savvy. Make things obvious for visitors. The more you hide things the more likely they are to leave you site in frustration. Testing the site with older users may well show up some obvious usability errors you have made in your design.
any web designers think that a Home button is over-egging usability features. After seeing many users struggle to get back to the Homepage on major websites I recommend a link to the Homepage in the main navigation.
Users are the most important thing on your site. You can indulge a design fetish or use the latest web technologies if you want to but do not lose perspective. Users are why you are making your website so if it does not work for them there is no point doing it.
Talk to users. They are the ones who define the success or otherwise of your site. The web is not a static medium so things can be changed. If you find that users are failing to find something or to perform a specific task then you should amend things. You will save money by fixing a problem before it gets out of hand.
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