depending on the target audience of your website you may also consider to make it as accessible as possible. there exit some standards from the w3c dealing with this issue (web accessibility initiative):
unfortunately it is not really possible to automatically test the complete accessibility as defined in the wai standards.
There exist several guidelines for web design. The most common ones are the W3C guidelines. Those define, how tables, fonts, colours etc. have to be designed to guarantee the creation of a high quality website. The best way to start is to roughly go through all those guidelines and pick those who seem to be necessary for the current project. Next you can look for code samples or great designed websites, like published in the book “web design index” by Günter Beer. Some sketches can help to find out, how the website shall look like. When you start creating the website, make sure to use XHTML and CSS, since this is the recommended W3C standard. When you’ve created the first version of your webdesign, you should test it’s usability with some test persons, that give you creative feedback so that you keep on improving the design. When you think that you’ve finished and considered the guidelines, you can check your website automatically with the help of the W3C validators, that can be found here: http://validator.w3.org/