Giving birth can be a very stressful experience for a woman, so you need to be completely calm. This may be an emotional rollercoaster but you have to handle it. You're about to see your partner in pain. Or there might be an emergency. You might get shouted at. Throughout all of this you have to exude the cool of George Clooney. Although turning up in a tuxedo isn't necessary.
Timing is everything
If everything has gone to plan, you're probably at the hospital with plenty of time to spare, so you can make yourself useful straight away by timing the contractions for her, recording the length of the contraction and the time between them. So make sure you have a watch with a second hand.
During the contractions she may seem distressed and in pain. This is where you must remain calm and talk her through. Look into her eyes and breathe with her. The last thing she needs is you running off to find a doctor or a nurse when she's in the middle of a contraction. If you do think you need the doctor or midwife, wait until the contraction has finished.
Once the medical staff are in attendance and the birth is under way proper, she's going to need you more than ever. Hold her hand, encourage her softly (shouts of "Go on my girl!" aren't required at this point, or any other for that matter) and look at her face. Yes, that's her under all the sweat-matted hair. Use regular eye contact, smile at her and keep telling her it'll be fine.
And don't run out of the building two seconds after the birth to text the world. Stay with her, get her a drink of water, tell her how great she was, and have a cuddle with your new baby. Right, now go and text the world.