Listed below are some useful and rather important tips for designing a professional and high quality web site:

• 
  Neat and Easy Navigation:
  Navigation of links on your site plays a big role in determining the
  stickiness of your site (how long your visitor stays and explores your
  site). Ask yourself this, what do visitors do as soon as they open your
  site? They would probably read the content of the present page and then
  look around to find any other page that interests them. Read our article
  on Web site Navigation Tips.
  
• 
  Clean Layout Design: A clean layout that uses a lot of white space enhances a site's looks. Try to keep the focus on your content, use dreamweaver templates for this. Use fonts that will be available on all computers to prevent your site looking messed up.
  
• Program using pure CSS:
  The world is moving away from table based websites to pure CSS websites
  because it offers accessibility, reusability and considerably reduces
  file size apart from giving greater control over the look of your
  website. The single most important skill you can learn today to become a
  quality web designer is CSS programming! Even if you are not an expert
  at CSS you can learn to use the following simple CSS Styles Effects to
  enhance your website:
  
  
  1. Cool Text Effects using CSS Styles: Text Links Rollover, Text Case Setting, Text Spacing and Line-through Effect
     
  2. Bullets in HTML or Deamweaver: Using CSS Styles with bullets (shapes, decimal, roman-numerals, images, etc.)
     
  3. Links without Underline: Use CSS Styles to display links without the appearance of the underline.
     
  
  


• 
  Optimum Load Time:
  Make sure your load time is low. For this you must:
  Minimize Graphics, Flash and scripts: They hugely increase your file size.
  Optimize your HTML & script code: Make sure that your site doesn't have any unwanted tags or unused scripts.
  Use Server Side Include (SSI) files where ever possible. SSI files once called from the web server reside in its cache so on subsequent requests they load faster.
  Read our article Tips for a Fast Loading Site for more.
  
• 
  Design for all Screen Resolutions:
  A site that is easy-to-use always encourages visitors to stay and read
  your content. For site with long pages of content this is very crucial
  as the amount of scrolling required is reduced. Suppose your site
  doesn't look good for a particular resolution it is very probable that
  the visitor will close the browser window feeling that the web page is
  not for their viewing. Designing stretch layouts that fit any screen
  resolution ensures that you know all your visitors see a visually
  appealing and professional site.
  Read our article Designing for all Screen Resolutions for more.
  
• 
  Ensure Web site scalability:
  Make sure your code and design is scalable. As technology advances and
  configuration of computers & their monitors keep increasing and
  varying it is impossible to test your site in all screen sizes and
  platforms.
  
• Cross Browser Compatible: Make sure you check your site for Internet Explorer 5 , Mozilla Firefox 1 , Opera 7 , Safari 3 and Netscape Navigator 6 as they constitute 95% of the world's browsers.