Sorry The 7th Sin I really don't think that tutorial would help Juniorps. You should approach this as you would do in any other art form, I suggest you use some good old fashioned observation and work on developing a better understanding of the shapes and depth. I think CodeCriminal has got this on the right track but I strongly suggest gathering a good variety of real life references, you can then at least work on emulating the correct shapes and work on making yourself much more familiar with what you want to portray.
But I do stress, if you're struggling to create convincing clouds really do go back to the bare basics of it, this should be in mind with everything you do. Break it down to the bare bones (possibly a simple silhouette) and built this up step by step, colour by colour whilst working closely with observations and the references you've gathered. If you jump straight into something too complex you'll find you'll lose any grasp of convincing shapes and depth you initially had..
Do you have any atempts to show, I think we would be able to offer much better advice with something visual to go off.
