Clipart is the niche that feeds every other niche
Other sellers buy clipart to build their own products, which means your file needs to be flexible: high enough resolution to print large, and available as a vector file for anyone who wants to resize or cut it. Building to a consistent, generous size from the start avoids remaking a bestseller later because a buyer needed it bigger than you sized it.
Sizes sorted, next is spotting which motifs are about to be in demand. Read how to find clipart and svg trends.