hello
i'd like to know the best way to animate advancing clouds, the way that produces the most realistic results
what about the "Cycling" and "Turbulence" parameters? What do they produce?

Cycling is best used with texture maps, it helps beak the repeating patterns when a bitmap is tiled onto an object. Global turbulence modifies the origin of a noise/fractal node and creates "wavy" patterns. It is not very interesting for cloud modification, because the scale is too smal, even if you change the size of the turbulence, you will only end up with small dots appearing in the cloud, like grains of sand. Adding turbulence in the fractal node, within the function editor can modify completely the function that defines the cloud shape, so check thoroughly  what you are doing. You can get interesting results. Render times will go up though.
Best to animate clouds is to simply define a rate of change in the atmopshere editor.
If you are using metaclouds, and not spectral layers, best is to move the spheres around inside the metacloud group, while globally moving the metacloud group in the sky as well.

thanks so much for this bruno, your input is so valuable...