It helps me to remember that my body is doing what it needs to and I can do nothing about it. Let it do its thing. Try to relax and control your breathing.
If it helps, this is what I do:
When I'm in labour I visualise a time-line, with a start and end, and notches inbetween. (OK, stay with me on this one). As each contraction comes and goes, I move along this line, each notch (each contraction) falls away as the contraction subsides.
I tell myself my body only has to deal with a certain number of contractions, so with each one I'm closer to being fully open.
There comes a point when things get going that you'll just zone out and that brings some comfort.
This stage is the painful stage. It stops when it stops, and then you start the next stage (the pushing bit) which isn't painful, but it is hard work.