Do you have any concept art for reference?
Shabby as in post apocalyptic/abandoned, or just shabby as in 'ghetto' kind of shabby?
Rubbish: bits of paper, wrappers, general garbage floating around always makes a street look down in the dumps. Perhaps weeds growing through the cracks in the floor and out of buildings. Broken windows. Stray cats and/or rats. Steam from sewers; always guaranteed to add to that smoggy look. Dim weather, to add to the effect.