Zoom in 100-200% to carefully inspect your photos. Look for sharp focus, chromatic aberration, artifacts, noise, sensor spots and dust spots. Look at the histogram to determine whether you have any clipping (blownout or black areas with no detail).
Your image has a white balance issue (too blue), a leaning horizon, chromatic aberration among the leaves of the tree, and possibly a focus issue, though the file you uploaded is pixelated and too small to determine whether sharp focus was attained.