The exposure is really good, both the grass and sky are correctly exposed. The composition is solid, maybe cropping the picture would be better but it’s good either way. The camera settings you used are decent too, f/8 to capture the whole landscape in focus and 1/500s shutter speed to mitigate camera shake. And lastly, the whole idea of the image is beautiful, bright blue sky and a green field with a little rainbow in the middle.
Ways to Improve the Image
Looking at this image it’s obvious that something is missing to give it that wow factor - That missing thing is contrast. There isn’t enough separation between the ground and the sky, especially between the sky and the clouds. Adding a bit of contrast would make the whole image more dramatic and give it more depth. The colours of the rainbow would also pop off the screen more.
In the image below I have edited the original by adding contrast and also some HDR improvements plus a vibrancy increase.
Cropping is a very important factor in photography. If you don’t frame the photo good while you’re taking it, you can crop