The first time I uploaded a header image (instead of the default text that Blogger automatically uses when you first start a blog) I was left with an image I really liked, but some rather nasty looking 'space' towards the left. Here's how to fix that :)

1. Upload your header image (Layout > Configure Header > Upload)

2. Go to Template Designer (Template > Customize) and click on the following in the top left of your screen: Advanced > Add CSS and add the following piece of code

.header-outer {
margin-left:260px;
}

Now you will need to adjust the “260″ value, depending on how large your header is, and how wide your blog is, so just play with the number until it looks right.  (the smaller the number, the more to the left your header will move, and the larger the number, the more your header will move to the right)