a friend showed me this great video by Scott Robertson on Youtube.
I find it better than Photoshop, because it has some built-in tools for drawing in perspective.
I looked at a photo of a cool car (cool to me, at least) and did a side-view study of it. Then I used Sketchbook Pro to plot my own perspective and get to drawing.
It was definitely out of my comfort-zone and I struggled in the beginning. But after I managed to get past the initial problems, it went quite well and was actually fun.
So, if you are having trouble with perspective and constructive drawing, give this a shot and tell me what you think.
All the best,