Basically, count the number of z-levels at the left and the number at the right of this platform. You can see you have 6 levels at the left and somewhere between 3 and 4 at the right. The red box is just kind of really confusing if you think about what's actually happening there. Stacking horizontal walls to make a vertical wall is dangerous because (if I can find a decent way to explain this) two stacked horizontal walls don't equal the height covered by the two flat tiles adjacent to them. This is hard to explain without showing you but hopefully that works.
edit: Also, whenever you have stairs, you need to change a z-level. This goes in the other direction as well; if you're changing a z-level you need stairs.
Next is the green rectangle. That mini-ledge looks a little weird because it doesn't attach to the wall right. There's nothing you can do because that's not how the tile was designed to be used, but you might be able to shift it town a tile and use the other side of the same ledge tiles and just make it a little bump decoration instead of a ledge.
Third is the blue arrow; the middle bridge needs to be move down so it attaches to the bottom ledge or up so it... OH I think I just got the design you were going for in the red rectangle. The middle bridge needs to be moved up two tiles or you need to use the wall boundaries (the "side" versions of the horizontal wall tiles I was talking about earlier) to give that outcrop it attaches to the visual context it needs. There are no sheer drops in Pokemon tiles, you need to have sides and bottoms to all of your cliffs and the bridge only covers the bottom in this case (although the "bottom" would obstruct the path under the bridge, so the bridge really needs to be moved up).
Fourth is the orange arrow. Two issues here. This area and the area to its right have a direct conflict in z-levels. The arrow's pointing to the end of a 2 z-level cliff, but those rocks attach to top of this cliff to a 1 z-level plateau. Also, related to the red rectangle, that upper square plateau shares a z-level with 7 different adjacent z-levels, so it needs some help. The second issue is more cosmetic and it's just that you might not want to cover the end of a wall. It makes things unclear and makes the design feel a bit undefined in that region. Just extend the bottom cliff out to the right and it'll solve the cosmetic part of the problem (although it will bring the z-level issue into sharper focus).
The fifth focus area is also mentioned below so go there for more info, but match your wall tiles and your floor tiles. This wall belongs next to a dark floor.
Last mention is this:
It's not possible for this to occur in nature (but it's how Bluerobin Cave looked until its second to last iteration, so I sympathize). The left and bottom right levels are just fine, but the overlap between the second and third parts makes it so that the second part is on a higher level but has no support on its upper half. Basically, the third part needs to extend underneath the second one all the way around, or if you want to keep the same amount of obstructed area, the boundaries need to be redefined so the second level is smaller and that upper left area is part of the third part.