Besides bringing harmony, uniformity and consistency to a design, patterns help create visual interest in an art piece. The easiest patterns to design are doodle patterns in particular, as they are simple drawings with abstract shapes that form a work of art. For a colorful doodle pattern, check out this piece of art from Inna Kaleniuk.
You can download this vector file for free, and easily edit in Adobe Illustrator. It comes in a color palette that includes yellow, orange, green, brown, and grey colors. However, you can pick the colors of your choice and use the pattern to decorate your personal items, such as your mobile phone cover, notebook hardcover, packaging or branding, interior design purposes, or even your UX and UI projects.