My rule #1, if there are bars on the windows, stay out of the neighborhood after dark. Lesson learned after I got lost on my bike one night, and ended up smack in the middle of Flint at 3 am. If you don't know Flint, think Detroit, but worse.
My other major rule is that if I'm carrying a lot of cash, I keep it in another pocket, rather than my wallet. Usually one of the inside pockets of my jacket.