Then most basic styling rules will be cross-browser friendly.
For the more advanced stuff like floating and dynamic sizing, always clear after using the float property to avoid height issues in firefox and text wrapping issues in old versions of IE.
And remember to test test test! Check out your page in each version of IE using http://www.my-debugbar.com/wiki/IETester/HomePage (windows only I'm afraid) and also see how it renders in firefox, opera, chrome, and safari, although the last 2 are usually pretty similar because they both use webkit.
One other helpful tip is when making a div, avoid adding padding to it as it will be inherited by the paragraphs, links, divs inside it as well. I find that if I add any padding required directly to the element in question - the paragraph or whatever inside it, it reduces cross-browser problems with how they handle inheritance. Also try to avoid state of the art effects, child selectors and the like.
BUT you can't use DD_Roundies AND a shadow on a div via the conditional statement methods above, due to the tricks the rounding script uses, so it's one or the other for IE I'm afraid. Text inside can have a shadow, I think, when using DD_Roundies.