Here is a little tutorial on my technique for painting clouds. I give you a few pointers and show my basic tool. I think the most important thing in painting clouds is to establish the source of light and stick to it. Inconsistencies here can really mess up otherwise good technique.
I hope you find it useful, if you have any questions let me know!
Examples: Also, I'm having an Anniversary Contest and Giveaway, check it out! [link]
<Note about the gradient of the sky: if it's pitch black in the middle of the night, then there might be no gradient, but generally assuming there is some kind of light source (stars, galaxy, moon etc) I find it more pleasing to the eye when you have at least a tiny shift of colour in the sky
>EDIT: Wow I never anticipated this tutorial could be so helpful to people, I'm really glad! It would be great to see your works!