The first 2 weeks was the hardest for me. However, it's important to never become complacent even after that and it's also helpful to understand what triggers you. Developing a sense of what triggers you to PMO or MO will help you learn how to better combat your urges. For me, the issue I still struggle with is seeing attractive women out in public and looking longer than I should, or even looking at all. I'm starting to combat this urge by applying a one look 2 second rule.
It's all about understanding your addiction. I myself never understood how addicted I was not only to porn, but to sex as well. Finding a Sex Addicts Anonymous group in your area is something I highly recommend. It has helped me tremendously.
We will always be addicts but we can learn how to manage and suppress our addiction and live healthy lives.