watch the light. you can have the best clouds ever, but if the light is hitting them at the wrong angle you'll end up with flat, lifeless crap.
these two shots were taken a day apart (similar skies and conditions on both days) within a few miles of each other. in the first the sun is nearly overhead coming just off camera at the top right (looking southeast). look at how the light is playing off of the mountains. it's flat and bland. if the light doesn't work on the land it won't work on the clouds.
this image was taken closer to golden hour, the sun was lower in the sky and i was looking northwest. the light is better on the mountains and so it's also better on the clouds. the clouds take on a more 3d look and the shadows on the backside of the clouds causes them to have more variation in color.
the camera settings were pretty similar between the two shots. one was 24mm, one was 28mm. both were taken with the same camera and lens. no cpl was used for either shot, i rarely use one. post processing was the same for both, i had to push the shadows and pull the highlights due to heavy smoke conditions from a wildfire in the park which was causing the sky to be brighter and blander than usual.
if there's a lot of contrast i'll take two photos, one exposed for the land and one exposed for the sky and blend the two by hand in photoshop. or i'll process the raw file twice, once for land and once for sky and blend the two in photoshop.