I had been working on a project that involved using oil paints-a medium I don't normally work in. I wanted to learn how to make clouds, so I went to You Tube and typed it in. I found two videos that I thought were pretty good. Maybe you'll gain something from it too:
This one is from an artist affiliated with Jerry's Artorama:
And this one, although done on a similar vein, is done by an artist not affiliated with any art supply company:
Perhaps you have not been successful in the past in painting clouds. I think with these two tutorials, you've got it made in the shade.