Paint the walls a solid color that complements your color scheme. Add polka dots on one wall or apply a wallpaper border around the room that has polka dots on it to establish the theme on the walls.
Include a couple pieces of round furniture to go with the theme, such as a bright round storage ottoman. A polka dotted couch might be too much in a living room, whereas a polka dotted chair or throw pillows will establish the theme without being too busy. Add polka dotted knobs to a dresser or paint polka dots on a nightstand in a large bedroom.
Include polka dot patterns in some of the linens in the room. Large polka dots on a comforter will continue the theme in a bedroom. Use a polka dotted valance or throw in a living room.
Hang peel-and-stick vinyl circles on one wall, using only large and medium circles to keep the decor on the same scale as the large room. If that's too much for you, hang round picture frames or mirrors on the wall. Paint polka dots on a large mirror frame if you want to mix it up.
Spread polka dot details throughout the room so your theme is unified and the entire room looks connected. For example, a polka dotted lampshade or vase can sit on a nightstand or side table with polka dotted throw pillows on the bed or sofa. Anchor the room with a polka dotted rug or a rug featuring a polka dot border.