Disclaimer: Do not read beyond this line in case your wife is standing over your shoulder.
I mean it...girls can be very touchy on these matters...
ok....
My advice:
Stay up at the head, talk and pat "you are so good", "great work honey" etc etc yada yada but DONT look down.
Trust me on this...you might feel very curious and you might want to see what it looks like...but for the love of everything holy, DONT look down there.
When my first kid arrived (after gf had had a neat 13-hour struggle with maraton vomiting and excruciating pain) I was too curious so I looked down there to see what it looked like/how it was going. It killed our sexlife for the next year or so, and I was this close to fainting *shows with thumb and finger*
This was of cource before the doctor used a pair of scissors to do something UNSPEAKABLE
I can give you details if you want, but trust me on this. Stay with the head, dont look down until they put the baby on her belly and everything will go just fine.