Hi,
We chose our agency because we had met a couple who adopted thru them. Also, a friend of ours is involved with the same agency--it was nice to have personal experiences to go from. If we were going to be living here, we would be using the agency again for the next child (we're moving out of country in November, so can't use our agency

)
If I had to do it cold, I would start by going to the various agencies and adoption attornies in your town. They should give you names of people who have used them in the past and you could speak with them. Also, if there are any adoption info gathering fairs....those would be good places to start. (I am speaking at our agency's info fair in October, sharing our story.)
One other thing that really helped me with our adoption journey was the book "Adoption after Infertility" by Pat Johnston (I believe that's her name.) It really helped me get my emotions in order, to help me put away the feelings I had about our infertility and helped me to get excited about how our family was going to grow thru adoption.
Good luck to you! I hope your wait is short and that your little one is in your arms soon.