This site has a lot of info about customizing your blog. It gives tips on:
Customizing Your Blog - Part 1 Gathering Patterns and Colors
Customizing Your Blog - Part 2 HTML Code
Customizing Your Blog - Part 3 Fonts
Customizing Your Blog - Part 4 Creating a New Header
Customizing Your Blog - Part 5 Adjusting Columns and Margins
Customizing Your Blog - Part 6 Adding a Signature and Personalizing Comments
You will also find a link that leads you to a tutorial on how to make a navigation bar.
creating a navigation bar
You know you've always wanted one :)