This is my first PS tutorial I've ever made, so have mercy :D
My explanations usually fail, so if there is something you don't understand, please ask me either in a PM or comment ^^
There are many ways to draw clouds, you can go creative and test different things. I only presented my own way.
The tutorial is pretty detailed, but there are still things I didn't talk about, even though I tried to write the basics.
The size of each page is somewhere around 1000x1500, so if something is not clear, feel free to download high resolution.
Oh yeah, you don't need a tablet for the clouds. Just wanted to point it out.
I use PS CS3, so there might be differences between the layout of my window/tools and yours.
I think this method can be used in GIMP/ Paint Tool SAI/ other software if you find the right tools/options.
When I finish the tutorial, I'll save a .pdf document and put here a link for downloading it, in case anyone needs it.