A banner should complement a blog's content, not distract or pull the reader's attention away from it. One key element to this is choosing the right overall size for the banner. Horizontally, the image should be as wide as the blog's container. We have more tips for choosing the width for a banner here.
Vertically, the image shouldn't extend beyond about 1/4th of the screen size when you first load the main page of your blog. Anything more than this forces the reader to scroll down to get to the content which can be distracting and in some cases even confusing. A good rule of thumb is to start with an image that's 200 pixels tall and adjust from there.
Quality matters, too
No matter how lovely the content of an image or drawing is, if it's pixelated, blurry, stretched out, or squished up, we would recommend opting for a different image of higher quality. The banner is the first thing a new visitor will see when they visit your blog - using a poor-quality image could send the wrong message about the quality of your content.
Choose your focus
You might be tempted to create a banner using your fifteen favorite images plus a fancy font plus drop shadows, blurred edges and every image filter at your disposal. Unless you're a graphic designer, this type of banner can be extremely hard to pull off.
Instead, consider focusing on just one or two favorite (high quality!) images and a simple but unique font for your blog's title. No one has ever gone wrong by keeping a design simple and elegant!
Some great resources
If you don't have your own image or drawing to use for your banner, you still have a lot of options. For free stock images, try stock.xchng or if you're willing to pay for stock imagery, iStockphoto has thousands and thousands of images to choose from.
Skout is a resource for designers looking for free fonts, stock photos and illustrations, color tools, and all manner of goodies.
We're here to lend a hand, of course. If you need help with a new blog banner, or improving your old one, contact the TypePad Services Team and we'll be happy to assist!