How draw objects properly in perspective?

First, draw your horizon line across the top of the page. Mark two vanishing points, as far apart as possible. Draw a short vertical line for the front corner of your box and then draw a construction line from the top and bottom of the line, to each vanishing point. Next draw a vertical line to the left of your 'front corner', between the top and bottom construction lines. From the top and bottom points of this line, draw construction lines back to the RIGHT vanishing point (VP2). Next, draw a similar vertical line to the right of your 'front corner', and from the top and bottom points of this line, draw construction lines back to the LEFT vanishing point (VP1). Where the top construction lines intersect, drop a vertical line to the intersection of the bottom construction lines - this will give you the back corner of the box. Erase the construction lines and any interior lines. A helpful website I have found regarding two point perspective: http://drawsketch.about.com/gi/dynamic/offsite.htm?site=http://mathforum.org/workshops/sum98/participants/sanders/TryPersp.gsp.html