You have your new blogging software set up and everything seems to work properly except the default look of the blog is nothing to brag home about. If you start digging, you’ll probably find that your blog software uses CSS in its design. Now you’ll have to figure out how to manipulate the CSS to give the look & feel that truly smacks of you. Here is a good starting point. Simon Willison wrote a very good introductory tutorial on the basic building blocks of a stylesheet with emphasis on the differences among rules, properties and selectors, and how to use them.
Simon also tutors on how to attach the newly created rules to a webpage using either internal or external stylesheets.