IMO the best thing you can do is know as much as you can.
Read everything about child birth, the good & the bad.
Prepare yourself for ANYTHING & everything.

The first time you have no idea what you are in for, so its really hard to be prepared.
The second time you get a shock as well, coz you don't think 2 labours could be so different.

Once you really know all that & if you are lucky enough to birth vaginally the first time without too much intervention you will have more confidence in your self to do it better next time.

I think that has alot to do with it in some cases.

It is so hard to know what you will be in for til it happens though. IME the pain gets to the point where you get scared & give in.
When you are in that much pain its to easy to give in & give up, so a strong support person is helpful!