Pour enough paint to complete your job into a 5-gallon plastic bucket. Use a high-quality, matte-finish latex paint for this application.
Add a small amount of ready-mix joint compound to the bucket and stir vigorously with a paint stir stick.
Continue to add joint compound in small amounts until the paint reaches the consistency of thick cake frosting.
Add a small amount of water to the bucket to thin the mixture. Continue to add water until the mixture reaches a "soft peak," similar to the consistency of whipped cream.
Apply the joint compound and paint mixture to your walls using a plaster trowel. Draw the trowel across the wall in long, straight strokes for a traditional look, or try curved strokes for a more contemporary look.