Here are a few suggestions and a visual.....
Your sky is quite strong...warm colors come forward, cooler ones recede. So your sky is trying to get in front of your foreground...
1. lighten the sky and add in some cool colors...
2 add some sky colors to the foreground for added harmony
3 determine a light source and darken the cactus on the off side
4 add some cast shadows to keep the cactus from 'floating...
5 try to wash out the line around the mountains and use color and value to differentiate shapes.....
Suggestions are overemphasized for demonstration...........
Forgive me for messing with your picture..........
It's a good start on a Southwesty pic.....
.........al