Hey there! :3

So firstly, I really like your terrain. You have nice variation, and a good amount of layers. I also like the 'decoration' you've given it, with the use of grass and flowers. In some areas, however, it might be a nice idea to add some wheat patches, just to fill the space some more so it's not so empty in patches! This also adds atmosphere, which I think is very important!

Secondly, organics. I really like your tree! I think it has a nice shape, and good decoration with the player heads. However, your leaves show an obvious sphere - try and hide this with percentages.
The most common command for tree leaves is usually:
//br sphere 90%air,10%leaves 5
Try that, and follow the branches first, then meet in the middle!
If you don't have branches, I'd highly recommend adding some.
The smaller trees I would make the trunks a little longer, so the don't look so small and chunky.

Lastly, structure. The one structure you have is pretty good, but I wouldn't use stairs to make the roof. I think for this style, you may want to opt for more of a medievally roof style, using full blocks instead of stairs. I'd suggest you bring the roof outwards, instead of upwards and in.

Good luck!
- Dutty :3