Doodling is simply drawing without a purpose in mind. Doodling is fun, and a great way to pass the time. No real direction is needed, but if you want your doodle to look really cool, follow these steps.
A scribble
First off, determine what kind of doodle you want to draw. Your imagination is the only limit, but common doodles include geometric shapes (like triangles or squares), faces, animals, houses, stairs, cartoon characters, hearts, musical notes, or something altogether more abstract. If nothing at all comes to mind, just put the pencil on the paper and start scribbling!
Step2
Bigger scribble
Now you have something on paper. Lets say it's just a scribble. The fun part of doodling is more doodling. Just keep going. Make another scribble just like it, then connect them together somehow.
Step3
Filled in scribble
Now you can fill in what you've already drawn. If you drew shapes, make smaller shapes inside it. If you made musical notes, draw in a scale behind them. If you just scribbled, then fill in your scribble with more scribbles. If a portion of your doodle resembles an animal or an object, draw it in. Make your doodles interact, draw things in front or behind, add shading if you like. Doodles only have to end when you run out of paper (or whatever you're doodling on). Enjoy your doodles!
Tips & Warnings
Sure it isn't artwork, but who cares? Doodling is just for fun!
There is an entire field of psychology called graphology, which is the study of handwriting. Apparently doodles play an important role in revealing our inner psyche.