well, first, you should find the horizon line on the enviro, don't search as hell, it's right in front of you, draw it on the canvas, then, try to find the vanishing points, and put them on the canvas ! be carreful, vanishing points are really far from each other, peoples tend to draw them too close, like both of them on the canvas, and it creates too much distortion ! you'll never have both of them in the canvas at the same time, exept in rare situation, there will be at least one in the canvas, and the other one far on the left or the right, or both out of the canvas ! with that, it'll be easy to set up a good perspetive! then you could begin by drawing the big shapes, continu with the small ones, and keep adding details until you think you've finished, and that's it ! Good luck with your work dude !
+1 for noah, he explained it well ! to be fully aware of how the vanishing points work, i think you should find some pics on google, about cityscapes, with a nice perspective, and find the vanishing points ( http://www.conceptart.org/forums/sho...d.php?t=108793 for more explanations ! ) C you man !