Looks like a case of too much contrast. In photoshop/gimp/whatever, try looking at a portion of the green things, and a sample of the cracked sky, the character etc. Look at the histograms of these. They each span a broad range of values, black or near black to white or near white.
Objects and background are easier for the eye to separate when their ranges of values don't overlap, or overlap a little. A light object with moderately contrasty detail will sit nicely in front of an all dark low-contrast background, and visa versa. But a medium value contrasty object over a medium value less contrasty background won't work so well, and never mind when foreground and background are both contrasty.
In your sample image, try repainting the green fuzzypuffs to be all somewhat lighter, darker. This will help, but this isn't the main problem. The tiles are very harshly contrasting. You want them visually in front, of course, but their very light texture with absolute black outlining draws visual attention away from all else, so your main character and the background tend to recede together in unimportance. These are not unimportant to our conscious minds, but at some level of visual processing in our eye/brain system, the relation of importance to object is lost.
Besides non-overlapping ranges of values and generally moderating contrast ranges, you can try well-separated ranges of color - bright red object over a watery blue/green background, for instance. Mario in KMSTR's linked-to image stands out by being saturated red, as well as being darker (not dark, just darker) than the surroundings.
The long-term general solution: take some informal art classes. Even experienced computer graphics experts can benefit from a bit of painting or charcoal drawing.