http://www.meago.deviantart.com/gallery/?q=cloud#/d20stzzJust look at pictures of real clouds, DONT USE BLUR! Draw loosely, if you know what that means, if not, it means just draw without giving a forget about where the brush goes. If you look at clouds really good artists draw, they rarely blur the stuff together, they slightly blend with the brush density settings a little low. When blending, I like using the darker color and the lighter color to make it look how i like. If im not making any sense, sorry.
just slap a bunch of colors around, clouds dont always look round in real life, make the bottoms a little flat.
try to not use white, use a blue-white color, and change the hue a little when doing shade, like a light blue cloud, shade it with a blue with a hint of purple
tl;dr just experiment