Previous posters have said some great things.

From my experience, just do whatever she wants you to do. Yes make sure you know her birth plan. My DP knew i didn't want any drugs and only wanted pain relief if it was absolutely necessary so when it came to being asked he spoke for me, if they pressed he basically told them to rack off. Reassure her that she is doing well, lots of encouragement does wonders. She may not want to be touched as i didn't want to be but having him by my side was wonderful. He also fed me water and wiped my forehead down which was great but your DW may not want that but it can't hurt to try.

Also when your DW is in the middle of pushing DON'T ask if she wants her hair out, my poor DP didn't know what to do or ask and he asked that and sure enough he got some very harsh words thrown at him! we still joke about it now.