The approach I have taken with my sons, is to talk to them about the pornography industry - the good and the bad. There is no point in just lecturing them and telling them never to watch it, that is neither realistic nor helpful. However, it is important that they understand that what they are watching, is usually a performance, and that means that the people involved are acting. They play parts and pretend. They do things that other people want to see, rather than things they want to do.
There are different types of porn out there and there is plenty of ethical and consensually made porn if you make a point of looking for it, but the industry itself is rife with abuse. Most, but not all is male directed.
What I want my kids to know, is that performed sex is not real sex, and there's huge chunks of the boring bits, that are cut out of porn. The bits where they get to know each other and talk about what they want to do and what they like. They miss out the foreplay and the small steps that couples make before jumping into bed with someone. You never see anyone changing their mind or saying no or anything going wrong.
They will watch porn and they will be influenced by it. The most important thing is that they understand consent, so they never pressure a girl into doing something she is not comfortable with.
There is a fantastic article HERE written by Stoya, which is what people need to know about having a healthy sex life in 8 common sense rules.
I completely understand all the issues with the industry and it does need cleaning up, but the solution is not a ban. It doesn't help to lump it all in together and claim that all porn is bad, because the definition of porn is far too broad. The truth is, that despite considering myself a feminist, I do enjoy watching some porn. I am quite choosy, and although there is violent porn available, I don't find it as abundant as the article would indicate. I also enjoy BDSM, which many people would view as violent, when I would view it as pleasurable. What other people need to understand, is that before that BDSM act took place, there was a conversation where rules and limits were agreed, and the act should never happen without that conversation happening first.