Using a paint roller, fill in all the blue sky leaving the cloud areas empty. Next we will start the clouds, I suggest you do steps 3-5 on one single cloud first, to get the hang of it.
Using a sponge fill in each cloud area with gray, creating a soft edge. These clouds will grow as you do this, since you want to completely cover any blue lines with a blurred edge. I used a brand new toilet wand I found at Dollar Tree, it is a 3-d sponge and perfect for this kind of work. The gray need to be a medium gray, no thunderstorms type gray. We will be eventually blending these two paints together. I used “Timber Wolf” with my valspar paint. You will be able to see some blue paint through the edges of your gray clouds, just as in nature. Don’t try to create a firm border, keep it wispy. It is starting to look like a painted sky right?