I recently re-designed my main website, and learned quite a bit about CSS and XHTML in the process. I also learned that there are a number of things you should do before re-designing a site, and thought I would list them here for folks who are looking to change their site layout:
- Validate your documents with a free validator
- See how your site loads in various browsers
- Sketch out how you want thing to look before you start coding
- Make sure to design with the future in mind (this especially applies to associating CSS classes with tags)
- Make sure you consult best practices
- Read a good CSS reference before you begin
- Make sure you integrate useful ads into your website (this will help cover hosting costs, which aren't free)
- Ask an expert what they like and dislike about your site
- Verify that your site doesn't have broken links
- Implement things iteratively (there is no need to do everything at once)
Keeping these things in mind will made re-designing your site quite a bit easier, and may even turn up some surprises that you weren't aware of.