1. Create a YouTube account
2. Upload videos regularly to YouTube, one a week is good enough.
3 .Become successful on YouTube. A decent number of your videos should have thousands of views each. There isn't a set limit but a good benchmark would be to have at least 1000 subscribers and over 100,000 upload views.
4. Interact with your subscribers. YouTube wants to see that there are comments on your videos, and an interaction going back and forth between you and your viewers.
5. Apply to the YouTube partners program by clicking here. Fill out the application completely, honestly, and putting yourself in a good light. The final decision can take anywhere from 1 day to a month, depending on your availability.
Hope it's useful to you.