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How do you prepare for becoming a dad?
You can't!!
As someone who is very good at preparing in times of high stress I can say with all honesty, I prepared my ass off, yet I was in no way prepared. The whole experience for me was a live demonstration of the saying that goes something like "plan for A future not THE future because you have no idea what THE future will actually be".
Listen to many and varied voices
I would say talking to as many people as you can and really mixing up who you talk to can be useful. Working as a Paramedic gave me a unique opportunity to interact with people from all demographics and I was able to take away little similarities amongst all no matter their back story.
Get building before the birth
I would also strongly suggest reading and pre-building all the 'baby stuff' prior to the arrival date and for the love of god read the manual. I have never been more stressed as when we first brought my son home and he started screaming the house down and I had to open, sterilise and put together the breast pump. This thing had a manual that was longer than a David Foster Wallace novel with instructions about as clear as Chinese algebra. Pre-build all the gear. You're not expected to use the breast pump but man you better know how it works!
Love, guilt and feeling powerless
The changes that happened to my wife were extremely eye opening for me as well. I felt a great deal of both powerlessness and guilt watching my wife as she struggled to feed while fighting mastitis, chronic fatigue, post caesarean healing and a loss of identity. I know for some that are autistic some of these strong and uncomfortable emotions are hard to sit with and a lot of the time I was either unaware of the feeling which I think mostly presented as anxiety, or I would preoccupy myself with stressors and fears and not simply just sit with my wife and acknowledge how hard it was. Often, I think this left her feeling somewhat alone in her struggle as I pushed to help and to ensure they were eating enough healthy food and sleeping in a safe manner. I often think back to this period and see myself hurting our relationship with love, just trying my best to 'treat' her discomfort and help but really making her feel judged, isolated and inadequate.
Seek out professional help
I would say to prepare for this period it would be wise to think about what demons you carry going into fatherhood and how can you best work with them at the time as they will sure as hell get louder and stronger at this time. I would suggest seeing a psychologist both alone as a dad, but also as a couple.
The way I see it you have two people, coming from their own worlds, carrying all their scars and their families scars and you put them together in a room. You ask each of them to take a piece of their heart, the most essential, important piece made up of pure hope and love. They both put those pieces in between each other and you have to completely let go. Then you're expected to raise this thing leaning on each of your own individual histories, which aren't always compatible, then you let this thing go out into the world to be bruised and battered by life!
Take the time to really understand each other and where you are coming from because after that kid arrives you will have neither the want or the will to do the work.
I would say the same for any challenges with ones physical lifestyle as well. If you have a poor diet or sleeping issues now do not expect them to get better with a baby !