Keep things in perspective...

These are some pages from the book Vanishing Point by Jason Cheeseman-Meyer. It is an excellent resource for all things perspective. I would HIGHLY recommend you get this book for reference. I still go back to mine very regularly to check myself. It also has a great section on curvilinear perspective for when you progress to that level, very neat stuff. Anyway, awesome book, you all should get a copy, you won't regret it I promise
This page illustrates how to progress through a one point perspective drawing. First start with two dimensional shapes, then project lines to the vanishing point to create the sense of depth.

This page explains much of the same thing as the one above it, however it is in two point perspective.
Not all great scenes or layouts need to be very complex, the image above shows this well. It has a very dynamic feel, despite being of simple construction. The lower image on the page presents the basic difference between one and two point perspectives.

These two pages go through one approach for creating a scene in perspective. Again while the finished product is very appealing and daunting, the elemental construction of the scene is very basic. An example of this and a great source of inspiration can be found at Feng Zhu Designs, go to the gallery and check out the environments. They are an awesome example of what can be done with these simple tools.

It may seem difficult to grasp now, but perspective is the cornerstone of all drawing. If you master this, the effectiveness of your sketches and drawings will improve tenfold. Keep workin at it!
-kurt-