1)The internet is a new medium.
At least compared to print, it is. A website is a waste if it simply re-hashes something which could easily be put into print. Don't have the site be just an online brochure. Put up features which take advantage of the internet as a medium of communication.
2) Design the site for customers, not the company.
Your site needs to satisfy the needs of customers, not the company. So, don't post content which is not really useful to the site's customer.
3)Don't Operate in a Cocoon.
The internet is a medium which is shared by millions. When you set up your website, don't operate as if you are a self-contained island. Get out there and keep in tune with what is happening on other websites related to your own. Participate in forums. Post links to other websites and ask for a link in return.
4)Have a Plan to Attract Repeat Traffic.
Use newsletters, out-going email, contests, forums, clubs, auctions – anything that will cause people to return to your website. When posting links to other websites, don't just send your visitors somewhere else. They may never return. Provide them an exit page. Give them a pop-up when they try to leave your site.
5)Track Your Visitors
Pay attention to your site's statistics and react accordingly. What are people reading? How are they finding your website? Do they just come and leave right from your homepage? How long as they are on your website? Do they return? This data is immensely valuable in fine-tuning your website based on customer needs and wants. Remember, the biggest mistake of any webmaster is designing the site for what THEY want. A successful website is designed for the target audience, not to impress the site's owner.