I have a couple of tips for you.
1. Do not shave the opposite way of the hair growth. I know it is tempting to, but don't.
2. Make sure that you don't have too much shaving cream on.
3. Make sure your razor isn't clogged.
4. Make sure that your razor is brand new/fairly new.
As for getting all of the hair off while shaving that area, it is almost impossible with a razor.
I suggest that you go get a professional wax.
If you decide to self wax, be very careful because that is a sensitive area.
Take care! (: