On Sep 23, 2020, at 9:21 AM, Jim Betz <jimbetz@...> wrote:

  2) Darker colors on the roof and lighter colors on the bottom.

As a rule of thumb, everything goes towards a mid-tone. Brianna, my daughter, and I gave a clinic at an SER NMRA annual convention when she was the tender age of 5. She had many things to contribute, but perhaps the most seminal was “If it is light, make it darker, and if it is dark, make it lighter”.  BTW, the old theater adage “don’t work with children and animals” is entirely true. Brianna stole the show. 

And no pressure, but if a 5-year old can weather cars, so can you ;)

  3) Cars sit more than they move - a lot more.  So any "streaks"
       need to be vertical rather than horizontal.

Except passenger cars and head end cars, which may have a more all-over weathering pattern, with some horizontal aspects. Locomotives also have patterns that both relate to gravity and movement.

  5) A final light dusting with an air brush helps a lot - I call this the
      "blending coat" - I usually use a very thin "weathered black" color
      for this but have also used just dullcoat and other such.

Vary this color to vary your weathering. Alternative are Harbor Mist Grey, Railroad tie brown, 

  6) Weathered equipment is never "shiny".

In real life, some equipment can retain a shine, whilst being weathered. However, I have never found that gloss looks anything but “toy-like” on a model, even if the prototype was shiny.

 10) Rust is a job best done sparingly.

And remember that there are infinite shades of rust.

P.S. There are many different 'methods' - I prefer acrylic washes.

        Some guys prefer pan pastels.  Some guys like to do it all
        using an air brush (I consider this to be the least successful).
        In the end you will develop your own 'process'.  Don't forget
        to vary what you do from car to car - such as the shade of
        this coat, how much of a particular coat you use, what order
        you do different steps, etc.

I try to use different methods to mix things up to avoid the everything looks the same problem, but also to build skills with different media.