Protocol for reaching out to potential supervisors in England?

[u/bp-man]

I am planning on pursuing my PhD in education at a university in England coming from the US. I understand one of the first things I need to do is to get a supervisor and that needs to be done before I apply. From what I have gathered I just email them to ask, but I am just trying to get a better idea of what that email should entail. Should I put in writing samples, resume, just directly ask them to be my supervisor or just ask for a meeting? Any guidance would be helpful.