Perspective problem need quick help

[xxPurple Nugxx]

I am doing the perspective lessons in succesful drawing by andrew loomis but he doesn't even talk about vanishing points, and im making a horizon line and putting the two vanishing points at opposite ends of the HL. Connecting lines from each VP they come out looking wrong. NEED HELP. Please help me understand vanishing points. Where should I put them?

[Mumph]

You need to create a 90 degree angle between the vanishing points (at the station point). (The volumes in the attached example does not have the same measurments.)

Basically, put them far away from eachother and draw inside the Cone of Vision, otherwise you will get warped perspective. Someone please correct me if i´m wrong. I´m also learning this stuff now.
I would highly recommend Carl Dobskys perspective tutorial (http://media.massiveblack.com/downloads.html#carl). Also check out the book "Perspective made easy" (http://www.amazon.com/Perspective-Made-Easy-Ernest-Norling/dp/9563100166/ref=sr_1_1?ie=UTF8&s=books&qid=1273390858&sr=8-1) by Ernest R. Norling.