1. Navigate to Feedburner.com and log in to your account.
2. Click the feed for which you want to put ads in email subscriptions.
3. Click the 'Monetize' tab and then click the 'sign in to Adsense' link. This will redirect you to your Google Adsense account page.
4. Click the 'Adsense Setup' tab and then click 'Adsense for Feeds'.
5. Select the type of Adsense unit you want, the frequency you want it to display in the email, position and color scheme.
6. Under the 'Feeds' heading, choose the feed you want. All feeds you have registered with Feedburner that do not currently have Adsense should be available. Click the 'Save' button to apply your changes.