1. Create a Google AdSense account. You can use the same Google account that you use for YouTube. Go to the AdSense website, enter your account information into the sign-in fields, and follow the on-screen account setup instructions. Once you have your AdSense account set up, you will need to wait for Google to send you an authorization code via postal mail. This code will need to be entered into your AdSense account in order for you to start receiving ad payments.
2. Create video content that does not include any audio or visual imagery from works that do not allow commercial use. You may be familiar with fair-use practices of audio and video sampling, but these cannot be used with YouTube videos that will be generating ad revenue. The only samples that you can use are those that fall under public domain or that are licensed under a Creative Commons license that allows for commercial remixing. Otherwise, all the audio and video content in your YouTube channel must be yours alone.
3. Amass thousands of viewers on your YouTube channel. YouTube does not specify how many viewers are necessary before a user becomes eligible for a partnership. The exception to this requirement is if you are a filmmaker who has a proven record of successful commercial sales, such as DVDs or digital downloads.
4. Submit a YouTube Partner application at YouTube's Partner website. If your account does not meet the specified criteria, this page will automatically redirect you to the main YouTube homepage. YouTube may take several days to inform you of your application status.