You have to "feel it inside" first. This is true for any photogrpahy subject, in any format. For example, if you want to capture the serenity of a peaceful landscape, you have to make yourself quiet inside first. Sometimes I'll sit down and chill out under the trees for a half an hour before I start shooting.

For a city, at least to me, it's opposite. When I want to shoot downtown in my city, I often start with a cappichino (spelling?) at Starbucks.

Once you get yourself into the mood, you stop thinking about it, and then just do it.

good luck
joe