I am a firm believer that usability and not the visual design, determine the success or failure of a website.  Basically, users' habits on the Web aren't that different from customers' habits in a store.  If you put obstacles in their way and make it hard for them to shop, they will leave your store empty- handed and never come back.

A fast loading website design is important if you want to keep a visitor on your site.  Many sites that require Flash Player to be installed so that fancy music and pictures can play across the screen, often don't make it past 15 seconds before the visitor clicks the "Back" button and goes somewhere else.

Ensure your site is browser compatible. Your web site should look good in multiple browsers including the most popular Mozilla Firefox, Safari and Internet Explorer.

Simple and neat designs are the most effective for the web. Don't be tempted to clutter your site, especially the Home page with big, bulky images that take ages to load.  Make use of white space as it gives a sense of spaciousness and overall neatness.

People, who visit your site, generally scan pages looking for an answer to a question or a solution to a problem.  An effective website will help answer the question and provide a solution to the problem.  Yet, many website make it difficult for visitors to find answers and even generate more questions. The more questions your website creates - where's the newsletter option, how do I see what's new, what is this companies product, how does delivery work, how do I get to the login page, where am I? - the more likely the visitor is to use the "Back" button to find a more useful website.

Your web-page and navigation menu should be obvious, self-explanatory to the customer and follow convention. Many businesses who start up a new website, try to distinguish themselves, not through product, but through how their website menus are presented.  I say stick to convention because it is one less question generated - "how do I use this menu?"

Read more:

1. Understanding your customers
2. Ensure your website is easy to navigate and use
3. Content is King!
4. Google Adwords - changing the way business market their products
5. Convert a visitor into a purchaser using a "Call-to-Action"