Those of you that think you can't draw probobly can draw whimsy stuff. The imperfections are what makes this style work. I would suggest drawing something twice as big as you want it, than outline your sketch in black and tape it to a window and trace changing any parts that annoy you. Repeat until you like it. Then use a copier to reduce it, which will often eliminate some unimportant details and simplify the design more.
If you can use a rotary cutter you can draw a straight line. It's almost the exact same process with a ruler and writing utinsel. I literally spent hours learning to draw a straight line in graphic design school and when I miscut I see its the exact same mistakes I make when drawing.