source: www.youtube.com
Mahalo drawing expert Ken O'Brien offers an exercise to help you draw straighter lines.
Instructions
1. Using a pen or Sharpie, draw several dots in random places on a piece of white paper. 
2. Connect any pair of dots with a straight line. Do it freehand, rather than using any kind of straight edge. Use a broad sketching motion. If you draw it too slowly, there is less of a chance that it will come out straight.
3. Continue making dots and connecting pairs. Try to connect as many dots as you can. This will give you lots of practice drawing straight lines, leading to greater line control. Straight lines are also useful when drawing square characters such as Spongebob Squarepants.References
Meet Our Expert
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Ken O'Brien
Ken studied at Cal Arts with a double major in art and animation, and later worked in the video game industry as a level designer for companies like WayForward Games and Activision, where his credits include Jake Long the American Dragon and Enemy Territory: Quake Wars, among others. O’Brien is a longtime Apple guru, working as a personal instructor of Apple software and products after his career in video games. In 2010 O’Brien started his own art blog, LunchBagDad, which features hand-drawn and painted lunch bags he initially created for his daughters.
