Dark edges, heavy vignettes. And make sure you have plenty of light. Our cameras had a flash, but was practically impossible to control the blast, so I gave up on that and waited until the sun came out.
We did a week on the built environment, a week on the natural environment and a week on the social. I enjoyed them all. The social environment was great fun, and no one turned me down when I asked if I could make a picture of them. What a friendly bunch.