That's a nice start

I think badger has some good suggestions.
I think it will be more helpful if you receive some directions, so I'll try to give you some suggestions and how:
- the waves are a bit large and make the trees and mountain look smallish; the default watershader is configured for ocean-like waves, of 10m. If you reduce the scale from 10 to, say, 1m and reduce roughness to 0.15-0.2 you should get better results.
- there's no surfacing/shore yet: create surface layer and set the altitude constraint of that surface layer to the same as your water level + some meters. The standard fuzzy zone is 200m, that's way too big. Reduce it to a metre or two and start from there. Use the "test colour" to check if the altitude constraint is ok.
Now create a fake stone shader and connect it as a child layer to the surface layer you just created. You should now have a kind of stonebed.
- the trees are very dark; go to your population in the nodenetwork and press the +symbol until you're into the internal network of the object.
There's likely a red shader called something like "leaf 1". Open it and increase the diffuse colour from 0.5 to 0.6 (to brighten it up) and increase the translucency from 0 to 0.7, for starters.
Render out and post again here and let's continue from there

Cheers,
Martin