I worked by a process of elimination!
Nothing in the top 50 (I'm a teacher and have seen some of the awful nicknames kids can get when they are one of 5 Bens in the same class for example), so that knocked out a lot of names from the start.
Second, I wanted a name that my daughter could change if she did not like it. Girls can be so funny about names and I know a lot of girls / women (myself included) who do not like their names, so I wanted to give her the option to choose a pet name if she wanted to.
Thirdly, I didn't want a name that would date. So I avoided anything really 'now' or that people would later say was so 'Noughties' like people do with Sharon and Karen of my generation.
That said, I did want something that fitted in with the general feel for now - nothing that would stand out too much.
Then I avoided any names that were to either extreme of the class divide. Nothing too pompous or naff. Just a nice normal name that most people have a pleasant perception of.
I wanted something that was feminine but not too girlie. So I avoided anything with a y/ie ending - not professional enough for your hard hitting buisness woman!
We also wanted (hubby more that me) names that didn't sound too off the wall or foreign - that the child would be spelling for the rest of their lives.
Once we narrowed all that down, we just went with something we liked.