I'd agree with Pete about the rivets
and the rust streaks.
Also, a "top tip" I use (from 00 modelling days) is to work from a photo if possible. It doesn't have to be the same loco/wagon etc, just something similar but in just about the same level of neglect that you're wanting to model.
You can see then just where the muck accumulates, paint fades, rust builds up etc and copy that rather than "make it up"
Mix dry bushing with thin washes for different effects and just keep at it. Like PCLR says - practice makes perfect!
PS. Looking forward to a finished shot of the coach!