HTML and CSS techniques
For all the effort you put into building your site, the most important thing to your users is how your site looks. Managing the inconsistencies in your theme for each browser, for each module, and for user selectable themes can be very challenging.
First you should familiarize yourself with basic Cascading Style Sheets (CSS) concepts. Review CSS Discuss or HTML dog for CSS resources. A good overview of the power of CSS can be seen at the CSS Zen Garden.
Forums:
Validate! Always. Validate XHTML 1.0 Strict.
And really, a validating, clean layout will work 90 % of the time. It will have easy fixes 9 % of the time and will require hard measures only 1 % of the time. Really!
Please ensure that you've
Please ensure that you've validated both the CSS and HTML for your website using W3C tools. It would be great to review your theme with both the WAVE and FAE accessibility evaluators too. There are also some other good validation tools.