Here are the guidelines (aka tutorials aka How-To-Add-Nuffnang-Ad Units-For-Newbies) linked from Nuffnang.
Anyway, here are some other tips when adding the Ad Units to your blog - only for Blogspot as it's the only blogging platform I've been using so far.
Leaderboard Ad Unit BELOW Blog Header
After inserting the Leaderboard Ad Unit code, the Ad Unit is located above your header. Sometimes the blog doesn't look nice with the Ad Unit first. Well, it you want to relocate the Leaderboard Ad Unit to below your header, here's how.
- Go to your Blogger dashboard
- Click manage: Layout
- Click 'Edit HTML' below the Layout tab
Then paste the Leaderboard Ad Unit code before this line:
There you go. The Ad Unit will appear below your blog header.
Skyscraper Ad Unit with Page Element