I drew this up right quick to illustrate a few perspective tips. A lot of people know how to use a horizon line to plot vanishing points, but a lot of times people don't really know how tall to make an item, or where to actually place the horizon. This can help make basic perspective a bit more practical.
Remember, wherever the horizon cuts, that's where everything will be cut, so it's much easier to gauge how tall something ought to be when you compare it to your character in the image.
And this stuff applies to any style, both cartoony and realistic!