Edit: Obligatory "Holy smokes DD"! Thanks all
You've got environments, and you've got characters to place in them...but what if they're all standing in different points in space? How do you make sure they all look as tall as they are, or aren't? How do you make sure you don't have cars the size of buildings in the background? How do you make sure your skyscrapers don't look seven feet tall? Read the tutorial!
This is a principle I've seen abused too frequently, so I thought I'd put together something on how to make sure your figures and environments all agree from a perspective standpoint.
Note that you can do most or all of this using lines and vanishing points, but this is an easy bit of shorthand to make sure figures stay in proportion to each other, or to use when you're sketching.
I think I learned the general idea from an old issue of Draw! magazine, but this was all done out of my head. Therefore, please don't repost this, in whole or in part. Please do download it for your own use.
Check out one of my old comic pages and see this principle being abused in action: [link]
(C) James Pray 2010