Mezzoblue's CSS Crib Sheet offers a bunch of quick tips to follow when designing using CSS (Cascading Style Sheets). Don't know what CSS is? This will get you started. It's a great way to design a site so that you can decide on style in one file and pull that "style" across to multiple files/sites - such as what I've done on the various music, blog, video pages on mennoboy.com.
Update: More good links care of scriptygoddess.com:The price of CSSWeb Redesign: a book to buyTables vs. CSSQuirksmode CSS HacksWill the browser display the rule?