While signed into your HonestGamers account and viewing any page on your blog, click "Settings" on the top bar to bring up a page where you can modify the general appearance of your blog, as well as your introductory bio and avatar.
You can make a selection so that your blog displays with either a white/light or a black/dark color scheme. You also can change the color of header bars that appear around the blog, and specify a background image. That image may either appear stretched across the width of your blog, or you can tile it (this works best if you have a pattern that you want to see repeat). You can also provide the URL of a 750Wx80H image to appear as your blog's header, which may be an image you submit to the site.
If you want to use a custom avatar, you can use the form to upload an image from your computer. If you don't take that step, the avatar that appears on the blog will be the same as the avatar you are using elsewhere on the site. Finally, you can provide a quick bio that appears at the top of the main page on your blog, so visitors can quickly get to know you before reading individual posts. It is a good idea to complete this bio, even if you don't get around to making any actual blog posts, especially if you are active on the site forums or if you contribute reviews.