I agree that faith in yourself is a huge factor!
I had gas & pethidine with DD1, because I had no idea what I was doing, or what to expect. I was terrified of the pain & thought it wasn't normal, so was fighting against it. Tencing my body up to fight the pain, rather than let the contractions do what they were meant to do.
Next time around I knew what I did wrong the first time, so I was able to focus on this. I tuned in to each contraction. Rather than freak out from the pain, I kinda hummed through them, while visualising what they were working towards - my cervix opening.
I think just the fact that this will be your second birth is a good start. You know what is happening, you have a good idea of what to expect & even though its still very scary, you know what is happening IS normal.
There are alot of great suggestions, but the first thing you need is belief in you You can do it xx