Improvement Tips

There are plenty of small things you can change about your web design which will radically alter the appearance of your site.

Here is a very compact list of what you can do:-

White space
Your web page should only contain information relevant to that page. By removing unnecessary items you can drastically increase the space available to you. This does not mean you should fill that white space with your relevant content. Mark Boulton published a great article entitled Whitespace.
Structural meaning
The elements of an (X)HTML document should have a meaning. If a viewer has CSS stylesheets disabled in their browser then the page should still make sense. Tantek Çelik has created an extremely useful presentation: The Elements Of Meaningful XHTML.
Cross browser checks
A major flaw in web design is to neglect older or less popular browsers. This is not to say you should check in every single browser or even in every version of popular browsers. However, you should consider checking browsers which you know your readers may be using. When I'm designing a website, I like to check the design in the two latest versions of Internet Explorer, Mozilla Firefox and Safari. By checking at least the last two versions you are hopefully covering the highest percentage of browsers in use. Johann C. Rocholl created a great way to check your site in many different browsers: Browsershots.
Validate it
Finally (and possibly most important) validation. If you have given your site a complete and exact structural meaning then it will validate perfectly. But we all make mistakes and sometimes you miss off that closing tag or put in a \ instead of a /. W3C offer a range of different validation tools from the Markup Validation service for HTML, XHTML, ... to CSS Validation. Check the Markup Validation Service for links to other validation they supply.

Thank you for reading and I hope these tips help.