Lay your paper plate flat on a table.
Take your washi tape or painters tape and start by sticking a straight line from the center of the plate to the edge, effectively cutting the plate in half. Repeat this to quarter the plate. You should now have a cross. Add two more tape lines to divide each quarter in half. Your plate should now look like it has 8 'slices', much like a pizza.
Now, start from the center and stick the tape in small straight lines that connect each of the large straight lines, mimicking the rings of a spider web. Repeat this 2-3 times, moving outward each time to create concentric web rings.
With your web design in place, dip your paintbrush in the watercolor paint and begin to paint over the entire plate. The taped areas will resist the paint, ensuring the design stays crisp. For a dynamic look, blend multiple colors or use varying shades.
Once you're done painting and while the paint is still a tad damp, slowly peel off the tape to reveal your striking white spider web against the colorful background. Allow the plate to dry fully.
For extra flair, you can glue on a little paper spider or even sprinkle some glitter over the web while the paint is still wet.