Yo again.
Some thoughts.Your trees were sparsely populated and they didn't take up much of their four tiles, which made it look like you could walk among them. I assumed this was not the case and made the trees take up more of the space and put trees in between trees to show this was a no-go-zone.
I created a hierarchy of your game objects using
contrast and a few other things.
The most important things are your characters. They go all the way from black to white, and have a side view. They take up a lot of their tiles and their large simple blocks make them stick out even more.
Next important thing is objects the player can collide with. The trees are a little dark because i just used rough outlines, but with thin outlines (and potentially no outlines) the trees and chest should be on more or less the same level of contrast. The chest though also uses a lot of it's tile, has a side view and has big, blocky colours to show it is more important than the trees, because it is collidable and interactive.
The trees then are the next important thing, but are shown to be part of the map with the angle and lots of colours gradually going into one another.
Then there is the long grass and mushrooms. Low priority and just there to look pretty, so a 3/4 view and not much contrast.
Finally the ground with low saturation, little detail and very low contrast.
You could take these concepts even further and tweak them to get the desired feel.
Remember that the most important thing about the art is to help the player play the game and focus where he needs to.
I'm really looking forward to what more you come up with. Keep up the good work!
(Also maybe update the topic subject, so that people know you're now working on tilesets and mockups.)