Perspective

This java applet pretty much explains 2 point perspective.

Here is a great turorial on perspective and basic drawing.

Here is a tutorial how to make a 2 point perspective grid in photoshop.

In landscape paintings getting the right perspective is essential for making it look real. I have read that the most important thing in matte painting is getting the perspective and the values right, so therefore I learn these two basics first.

btw the Vanishing Point tool in photoshop can be a great tool for placing/cloning textures in perspective.