Because you’re using a low opacity, the more often you touch the tablet (or click the mouse), the more solid the colour will become, so use increasingly less pressure to eventually define the edge of the cloud on only one side – the top. Use reference images or real clouds to make sure your cloud remains as realistic as possible.
Now download Bittbox’s free splatter brush set from this URL: www.tinyurl.com/2a6yvq. Use a couple of the brushes to add some colour intensity to the highest points of the clouds. Keep the splatter’s colour identical to the tip of the clouds. Erase unneeded portions and make sure they keep the same orientation as the other elements.
Using the same technique, apply some more splatters to the letter’s faces. I suggest using one on the first, third and fifth letter, so that the area doesn’t become cluttered. Also, add two soft shades of green with a large, soft brush behind the clouds. We’re doing this to chromatically balance the composition.
Now it’s time to add a texture. However, rather than adding a photo with a blending mode, we’ll apply only certain parts of a given texture. Download the watercolour texture image available for free from stock.xchng from this URL: www.tinyurl.com/65neat. Bump up its contrast by a hefty amount using a levels adjustment layer.