My little one is just over a week old and my DP has been amazing, so some tips from me:
Make sure she feels loved, wanted and attractive for who she is, not just for being pregnant - i found that to a lot of people I stopped being me, and just became 'pregnant person'. my DP made sure to keep reminding me he loved me for me, talked about stuff that wasnt baby related etc.
Be prepared to do everything in the early days. I made a cup of coffee the other day. It was both a massive achievement and a total ballache as i had DS in my arms the whole time. Its so much easier on me if DP is here to help, and as i'm shattered and sore, i do need that help.
Don't push her for sex. (obvious i know) But be sure to maintain intimacy, where you can. kisses and cuddles, massages with no further intent behind them etc other than showing affection go a long way.
Don't mollycoddle her. She knows her limits. Just make sure help is there whenever she needs it.
Know what stuff is and how it works, and when you will need it. My dp has apparently been paying close attention because yesterday morning he brought me a box of six tubes of lansinoh nipple cream, which he'd ordered online for me. He knew I would need it and went ahead and ordered it. Things like that mean a lot and are truly helpful.
In the delivery room, there may come a point where she feels like giving up. Be strong. Tell her how strong she is, how amazing she is and how much you believe in her. Tell her she can do it and keep telling her that after the baby is here and it gets really tough.
good luck, and enjoy every moment, it really is magical.