If you're working on a painting which just doesn't want to go right, one of the things you should consider is whether the elements (objects) in the painting are in the correct positions. An easy way to test this is to cut out the shapes from either paper or card and then try them out in various locations on the painting. It's certainly a lot easier and faster than painting something in and then scrubbing it out again if it's not.
You can also use cutouts to test the position of all the elements in a painting. Think of it as an initial step like sketching out a composition. You could do something similar on a computer too, in a painting program where you can sketch out the elements and move them around endlessly until you've got a composition that pleases you.
In the example shown here, the sky of the painting was too empty and your attention stayed anchored at the bottom of the painting with the trees and ground. There simply wasn't enough interest in the blue to get your eye to move up into it. I found a reference photo I had taken of a vulture flying, then printed and cut it out.
Then I tried it out in various positions to see where it would work best. I stuck it temporarily to the painting with some poster putty so I could step back and view the new composition from a distance. Putting the vulture on the right did bring your eye up into the top of the painting, but the right-hand side dominated too much also have two trees on that side.
Putting the vulture towards the left created a better balance, but in it needed to be higher up, rather than lower. Once I'd decided where I wanted to put the vulture, I marked it lightly in pencil, removed the cutout and painted it in.