1) Keep the raw file (e.g. psd, ai, cdr) in RGB format. Create the site design with the original dimensions (e.g. for 800x600=780, for 1024, 768=970).
2) Try to keep text and images separate. Avoid overlapping of separate elements.
3) Keep text content more than image.
4) Always use web fonts like: Arial, Helvetica, Times New Roman, Courier New / Courier so that design at execution won’t look different from raw file.
5) Put some textual content and links in bottom of every page (e.g. copyright, sitemap, ).
6) Usage of Headings is also good practice.
7) Avoid using lot of graphics or images that are hard to load, instead use a thumbnail to show and a new page (or popup) to view full image.
8) Headline plays a significant role in attracting customers. Hence use catchy phrases for the headline, it'll work well.
9) The most important is the content. Relevant content is the best way to keep the visitors hooked up and more over buy what you are selling. Correct use of words and sentences not only attracts the prospects but also helps the search engines to crawl it easily. Proper content, with relevant use of keywords is a MUST.
10) Determine the site navigation and its appearance before start designing. Also keep in mind we must use text as navigation, in case text is not possible images can be used but they must be small in size(kb), so that it wont take time to load.(Refer to yahoo home page).
11) User must should know where currently in site he is, show this by a textual bar like YOU ARE HERE
12) Avoid using gradient images in html page background, because it conflicts with site content and images at different screen resolutions.
13) Determine html link style (mouse over, normal) color and size.