If a character is smart, give them a giant forehead.

Practice "sketching light." Draw dozens of circles and squares without pressing hard. The Power of Exaggeration Realism is the enemy of cartooning.

A set of 2B pencils and a fine-liner pen (like a Micron) for "inking."

If they are surprised, bug their eyes out.

Should I include a for a specific character? paper and pencil ? I can tailor the advice to fit your specific audience .