Hey there!

So first of all, your terrain.
I think it's okay, apart from the squarish area you have on top with the water - that just looks way too man made, try and make it look a little more organic, with more random shaping than a square.

Secondly, organics - I like the tree, however I think you're going to need to make the trunk taller, instead of hanve the leave practically on the roots like they are now.

Lastly, structure. The structure you have is made from sand. This just seems a little unusual to me.
You'll want to start by making simple depth with the use of a frame. Depth is the use of layers. Simple depth is created through the use of a frame. A frame can be made simply, or it can be more creative.
Simple frame:  https://imgur.com/ONsoRxh
More complex frame: https://imgur.com/20eZjP8
Those are just two examples, with no palette, to demonstrate the difference that can make. You can use that on all four walls and make a small house, or you can make a larger structure with the more complex frame in the image.
However, these are both very basic still, we want you to be as creative as you can be!

Then you'll want to use a palette, it can be basic or it can be complex, but for a small house I wouldn't exceed more than three/four block types. You'll also need to detail - have a fly around the spawn and check out some of the plots in the black carpets - they're the exceptional ones of the server, we don't expect this standard, but they're good to help and inspire.

Good luck!
- Dutty :3