The answer that no one likes to hear is “practice, practice, practice.” I wish there was some magical shortcut for learning how to draw, but there isn’t.
I learn something new every time I drag my stylus or finger across the iPad’s screen. The best way to improve your craft is by putting in the time through observation and experimentation.
Dual majoring in graphic design and illustration at the Rochester Institute of Technology with a minor in fine art, certainly helped as I took numerous drawing and painting classes. I have found memories of lugging huge 18 × 24" pads of newsprint around campus to figure drawing classes where I learned the fundamentals of capturing 3-dimensional forms from hours of sketching live models.
After graduating college I stopped practicing and found my drawing skills got really rust from laying dormant for 13 years. To get my skills back in shape I started a 365 project a few years ago after buying an iPad and discovering Paper by FiftyThree.
Drawing everyday certainly helped me advance my skills, but I still have a lot to learn.