That's a good start for layout, something that might help is to look for a style you like from a specific game. Then try to recreate the style, not copy, but recreate it on your own textures.
Hope you don't mind me messing with your work, but you have made a good start it just needs to be pushed further. I added some highlights around the edges of the stones and made the crevices between slabs darker to boost contrast. Some of those cracks are a bit too dark so maybe lighten them up a tad. A bit of colour variation goes a long way so I just made a selection over each stone and played with hue/saturation but using a colour layer on top is also a good way of doing it.
But as StephLee said, the best thing to do is probably go and find some nice textures you like and try to emulate what they have done.
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It has a long way to go yet, keep trying.
But as StephLee said, the best thing to do is probably go and find some nice textures you like and try to emulate what they have done.