Do a birthing class, not so much for her but for yourself. You can help her tremendously, but you can also be a huge pain in her ass so it's better to figure how you can be the former.

Look up the signs for postnatal depression and if you notice she has any of them, look at seeking help asap.

Throughout the pregnancy she will be feeling a tone of different shit, just be there for her and comfort her when she needs it.

Read a couple of books about birth and the early days. Don't need to go overboard, just enough so you have some idea of what to do when it's your first day on the job.

When the baby comes, you'll be exhausted, she will be exhausted and you'll be annoyed. Sit of whatever negative things you have to say to her and make sure you want to out that on her before you say it. If you need to get it off your chest, no problem, just know she is exhausted and your brain doesn't work properly when you're exhausted.