I didn't have a birth plan & to be honest i think as someone else said, going into it with an open mind is the best thing to do. With my first (i was induced at 39 weeks) I was having really strong contractions but wasn't dilating, they tried me on gas and air but it made me throw up, the tried a pethadone (i think thats right) injection which had little to no effect and eventually gave me an epidural.
This time round i'm planning on going natural, so have soothing music, hot water bottles, cold face sprays at the ready, I'm already practicing my breathing and doing a bit of meditation - having said that depending on how much pain this little one wants to put me through, i may opt for something a bit stronger.