I think you are being too hard on yourself, but I understand -- I feel the same way about my paintings.
The answer is simple - keep painting.
I have been painting for a little over a year and share your frustration with not knowing what strokes to use to paint what I see in front of me and what I see in my mind.
But I do know that my clouds have improved over the last year as a result of trying and trying and trying again. I look at all the paintings here on WC in acrylics, the landscape forum, the marine forum and the plein air forum. I read the critiques for each one. I pour over instructional art books and watch videos on YouTube. With each reading and each viewing, I pick up one little helpful hint.
One thing that has helped me is to experiment with different brush shapes and sizes - flats, brights, filberts and rounds. Synthetic and bristle. Using mediums/gels with the paint and not using them. Every experiment with different combinations of brush shapes, brush types, paints and mediums teaches me something.
Unlike all the advice I have read, I have found that a medium sized round brush works better for me in attempting clouds... and using medium helps too because I can blend more easily.
Onward and upward we go.
Do your 120 paint challenge --- that's the best thing you can do. And keep posting your attempts for some helpful advice from more experienced painters than I am......
You've done a nice job on the foreground rock and you have the basic idea of the clouds right - with the darker gray on the underside and the highlights on the top...
One thing to keep in mind is that the sizes of clouds get smaller as you go down towards the horizon and the clouds get closer to each other as you reach the horizon (because they are farther away so we see them as smaller and closer together). The farther clouds will also be more muted in color than the nearer/higher ones...
The best videos that I have found on YouTube are by Jim Ingraham. Here's the link.
If you watch Beached Whaler #s 2a, 2b, 3 and 4 you'll see how he paints clouds.
He uses oil paints, so it doesn't translate exactly for those of us using acrylics, but I have still learned a lot from all of his videos.
Hope that helps.