Construction: draw the skeleton before the skin
Every cartoon character is built from simple 3D forms — a ball for the head, a bean for the torso, tubes for limbs — drawn lightly first and detailed second. Construction is why Bill Watterson could draw Calvin from any angle: he wasn't drawing a picture of Calvin, he was drawing a set of shapes he knew by heart. Exercise: draw a ball, then a ball with a cross on it showing which way it faces, then twenty of them facing different ways. Add features last.
Line weight: thick where it matters
A drawing with one uniform line looks flat. Cartoonists vary line thickness on purpose: heavier on the underside of forms and where things touch the ground, thinner for details and things far away, heaviest of all around the outer silhouette. Look at a Peanuts strip — Schulz's outline is thick, his facial lines whisper-thin. Exercise: draw the same simple character three times with a felt-tip: all thin, all thick, then thick outside and thin inside. The third one will look finished.
Inking: pen or brush
Pencils are for thinking; ink is for committing. Technical pens (0.3 to 0.8 mm) give a clean, even line that suits geometric styles like Dilbert. A brush or brush pen gives the lively swelling line of Pogo or Calvin and Hobbes, and takes months to control. Start with a fine-liner and a brush pen, and ink over your pencil lines in confident single strokes — a hesitant line inked slowly always looks hesitant. Mistakes get fixed with white paint, not by drawing over them.
Shading: hatching and spot blacks
Strips are mostly black on white, so tone comes from lines. Hatching (parallel lines) and cross-hatching darken an area gradually; spot blacks — solid black shapes for hair, shadows or a night sky — give a panel weight and pull the eye where you want it. The rule of thumb: one strong black shape per panel, placed near the thing the reader should look at. Exercise: take a finished panel and photocopy it three times; add spot blacks in three different places and see how the focus moves.
Contour versus gesture
Contour drawing traces the edges slowly and teaches you to see. Gesture drawing captures the whole pose in seconds and teaches you to feel. Cartoonists need both: gesture for lively poses, contour for clean finished lines. Alternate them — a page of 30-second gestures, then one careful five-minute contour of your own hand.
Simple color
Sunday strips and webcomics use color, but rarely much of it. Pick a limited palette — three or four flat colors plus black — and give each main character one signature color (Charlie Brown's yellow, Garfield's orange). Flat fills with a slightly darker shade for shadow are all most strips ever use. Anything fancier competes with the joke.
Paper or pixels?
Both are fine; the techniques are identical. On paper: smooth Bristol board, a blue pencil for construction (it doesn't show when scanned), then ink. Digitally: Krita is free and excellent, and a cheap tablet is enough. Whatever you use, draw at least twice the size you'll publish at — shrinking a drawing hides wobbles; enlarging one exposes them.
Next: how to draw a cartoon face, or go back to the cartooning lessons overview.