1. Leave your url on the comment page.
2. Add my blog to your bloglist. (By the time I visit your blog to make the lay-out for your banner ad, I will also check if my blog is on your list.)
3. Make a short post about this on your blog.
That's it! Very easy, right? And I want to add that this is "First Come, First Serve"
And once your post get expired, you can always come back to enlist your url again.