In short, the best way to learn to draw is to draw. I've got another blog called Michelle's Drawings where I was posting quick drawings. I've started adding to it again. Having my students draw every day worked very well for me at my first teaching job at a high school. One of my students even gave me a thank you for teaching him how to draw.
I learned about this technique from Kyle, a co-teacher at that first job. He attended grad school at Parsons, and got it from there if I remember correctly (which may be possible.)
Kyle called it a four-minute burn. First you choose an object to draw. That's essential to the learning process, that you choose a three-dimensional object to observe. Next you choose a pencil, or in my case a colored pencil. I like to keep the possibility of erasing my mistakes to a minimum.
Next you draw a format. This just gives you a rectangle or square in which to place your objects. It helps you to start thinking about where things should go in your drawing, also known as composition. After you draw the rectangle, start the clock and draw for four minutes. Don't erase anything, and don't try to make it perfect.
After you finish drawing for four-minutes, write the date and give it a title. If you can, scan the image and post it online and put a link in the comments if you try this so I can see what you did.
I have a small journal that I made specifically for my four minute burn drawings. It's almost full now, so I'll be making another one soon. When I make the other journal, I'll post some photos of it.
Here's my newest four-minute burn: