1. Something I didn't spot originally, your mountains are not level. If you look at the section I have circled it somehow overlaps the rest of the mountain, but meets the ground at the same place. When doing mountains the best thing to do is to map layer-by-layer, to help avoid this. You might also want to make the edge of the mountain more jagged, less uniform and straight to give it a more natural look.
2. I've circled some of the long grass, this type of grass does not match the map, imo. It's normally used in wet environments (so, near water) and should be used en mass rather than small patches. Stick with small grass for this map.
3. I've circled one of the pathways. If you look here you can see that (a) the path is narrow almost constantly 1.5 blocks, as the tops of the trees cover some of the bottom. The best thing to do would to make it more irregular and also one tile wider. (b) the majority of this map can be transversed by holding down a button - especially this circled big, it's one straight line.
4+5, on the right hand side, link back to these trees. For one thing, the two types of tree you have at the bottom do not mesh well together - one is a large tree, the other is a smaller, mangrove shrub thing. I would recommend sticking to the larger tree - another flaw with the smaller, R/S tree is how bad it looks when you have them linked together - it makes anything past the first layer look like a carpet of trees and exceptionally boring.
I'm afraid it's been a while since I've mapped, so I don't have any fresh examples, but
this map kind of shows a less uniform tree line. Many of the trees are at different levels, there are also 'side' paths (such as a surfable area) and a ledge to mean the map is different depending on your direction.
I hope that this helps and isn't just tedious to read.