Once you have installed your blog you need to choose and install your theme. I personally use KVModus.com, and search for WordPress Themes under the Category drop down option.
Choose the theme of your choice and then to install it, log in to your WordPress Admin and on the sidebar you should see a tab called appearance, then click Add New Theme. Once there, go to the top and click Upload, find your theme file and click Install Now. To set it as your theme, go to Themes and activate it.
