I tried to make sure my hands weren't clenched, read somewhere "make sure the uterus is the only muscle that's contracting".
Whenever I felt like "I can't", I tried to remember, "I can, and I am".
I also imagined getting to the top of a steep hill, and riding a massive wave - each one bringing you closer to shore.
"Each one done is one you don't have to do again"
"Each contraction is one closer to meeting your baby"
If all else was failing, I tried to focus on the fact that it would end!
I listened to the natal hypnotherapy CDs, and they had some good imagery - " the intensity of a contraction is like feeling the sun getting hotter on you, then going behind a cloud".
TBH, I couldn't have got through labour without yoga breathing/making controlled sounds/humming on the outbreath - sounds hippy but worked for me!
Good luck!