How would you prepare yourself mentally and physically to go unmedicated?
Educate yourself. That's the Biggest way to prepare. Read LOTS of natural birth stories, homebirth stories, unassisted birth stories... Talk to a midwife and get her perspective on birth, talk to other moms who've had natural births...
I spent a Lot of time online reading homebirth, waterbirth, and unassisted birth stories during the last trimesters of my last 3 babies. It helped Immensely... It helps you get into the mindset of "hey, this is Natural! This is the way it's Supposed to be! I can do this!"
Also, educate yourself about different varieties of caregivers, hospitals/birthing centers, etc. Different personalities and desires of pregnant women are going to be more comfortable in different settings.
If you want to have an unmedicated natural birth with little to no interventions, can't stand hospitals, and don't tolerate people telling you what to do, then you Really should Not be in a hospital... Maybe looking into a homebirth, or birthing in a birthing center as another option.
If you are ok with, or can ignore, medical personnel talking to you during labor, and don't mind the hospital regulations, then you would do ok in the hospital (or birthing center as an option).
If you want an OB telling you what to do the entire pregnancy, labor, and birth, don't mind being poked and prodded and having tests run, and Want to have everything micromanaged, then you would definately be the most comfortable in the hospital with an OB who loves to micromanage.
There is nothing wrong with
Any of these scenarios (or anything inbetween), you just need to educate yourself and see where you fit.
My experiences in the last 10 yrs:
I had a midwife in the hospital with my 9 yr old. That was a good experience, but it was DH who insisted on the hospital part (and that hospital sucked, which he admitted later.

)
When I had my 7 yr old, DH realized that a homebirth with a midwife would be completely workable (we bartered with her for part of her fee), so that's what I did. I LOVED it~ home water birth.
When I had my 5 yr old, our insurance changed and it was waaaayyyy cheaper for us to have her in the hospital, so I found an OB who was Completely cool with me doing everything MY way. That was a good experience (I ended up having her Unassisted In the hospital! lol), but I got irritated with the hospital staff.
This time, once again, because of the cost of midwife ($2500) vs what the insurance is going to pay (our out of pocket total this time is going to be $300 for both me & the baby. Total~ doctor, hospital, everything) I really don't have much choice but to do the hospital thing again. I have to tell you I'm NOT looking forward to that at all. However, I think I've found another OB who is ok with me doing things my way... As long as I can continue to bend him to my will, we'll be ok.

LOL
It's harder as a first-time mom to know how you will react to labor. I have been through it so many times I know how I am... I get very quiet and go "inside", close my eyes, and want to be left alone. I get irritated with hospital people messing with me, and don't usually even allow them to check dilation. Dilation doesn't mean as much as how Stretchy the cervix is. They know this, but they still want to micromanage everything. Anyway, because of knowing how I am, I Have to have a caregiver who understands me and trusts me.
HTH~