CSS (Cascading Style Sheet) is not very difficult to learn. The hardest thing is to ensure the CSS layout being displayed identically among different browsers. Even though CSS3 will be released soon, but I believe it will take quite a long time for all the browsers to start supporting it, especially all the old browsers like Internet Explorer 6 *AHEM*.
Right, here is a list of CSS tips and tricks that I believe will help you! You might also want to use some of the tools that will help you in web design and development - 22 extremely useful tools for web designers and developers