Is there a reason it is symmetrical?
The plants and stuff don't need to be that straight, maybe make the cave wider and spread things out more.
The layout is good but it seems a little narrow and long. Also the beginning left and the right side seem a little... too straight.?
The walls also seem a little bare, maybe add different wall tiles and some vines?
(You can find vines in various rtp tilesets, it has a nice effect on caves)
Also the floor is kinda plain. I would use the path and the shadow dirt autotiles to make it less plain, or maybe add some water. But I don't recommend water as it's the entrance.
Also with the way your going now, I see no light. It's a cave so it's going to be dark.
Maybe use a picture overlay with holes through the roof and it shines down or make a fire or torches.
Unless of course your character can carry artificial light.
What else...
Oh! You use a lot of crystals, I would focus on plants mainly or rocks. (As you don't really see a lot of crystals in caves. Well where I live you don't
)
Also I would extend the middle part to make it where if your on the left side you won't see the right entrance. That way it makes it where the player wants to explore both parts to see if he/she is missing anything.
Also, since it's the entrance your going to have light coming in from the entrance unless it's dark outside of course.
Hope that helps somewhat (: