If you're using AdSense in your sidebar or header (two relatively popular spots in WordPress templates) you need to be aware that Google prohibits the placement of AdSense blocks on Error pages. If you're using a custom 404 page this can pose a problem. The trick here, of course, is that you want to make sure you keep your ads on every other page - but you don't want them appearing on your 404 pages.

Luckily WordPress has a series of "Conditional Tags" that can help you overcome this dilemma. Read the Rest of this post