Draw a circle on a piece of plastic, using a compass. Cut the circle out with a craft knife to make a stencil. If purchasing commercial stencils, you may skip this step.
Lay a drop cloth under your painting area to protect the floor and cover trim with masking tape.
Wash the wall you wish to paint with soap and water to remove dirt and grease. Allow the moisture to dry before proceeding.
Fill a paint tray with the color you want for your polka dots.
Place the stencil on the wall where you want a polka dot. Secure the edges of the stencil with masking tape to hold it flat.
Sand the negative space inside the stencil to promote paint adhesion. Blow away the sanding debris.
Dip a flat-tipped brush in the paint and swirl it on a paper towel to remove excess paint.
Swirl or stipple the brush inside the stencil's negative space, overlapping the inside edges of the stencil to make a perfect circle.
Remove the stencil from the wall while the paint is still wet and secure it where you want the next polka dot to go. Repeat the stenciling process until the wall is filled with polka dots.