I'm going to have to go with Da Vinci here and sure I've mentioned him before, but if you're going to emulate, you might as well pick a well rounded master. There's some great advice for everyone in THINK LIKE DA VINCI, which says you should start by drawing a little every day in a notebook.

Don't worry if you're not any good. Who would be just starting out? Hold the pencil gently and try to draw shapes. Circles, squares, cylanders, and triangles. Practice wavy lines. Draw lines over and over again, filling page after page in your sketchbook with just lines.

This is muscle memory, and will get you prepared for the next step, which is to combine the shapes and lines into images. Eyes are just ovals. Pupils circles. A chin is a wavy line, as is a beard, and hair, and eyebrows. Lips? A curve. Crow's feet? Lines.

How about a house? Just draw straight lines.

It was really amazing how he broke everythign down into sketching lines. To think, THE LAST SUPPER or MONA LISA started as sketches in a notebook that translated to charcoal marks on canvas, and they were just lines that became masterpieces.

Practice lines and shapes. Don't worry about technique or even how it looks. Just draw. And keep drawing every day.