Hi @ArtistErin I'm sure you'll find a way of establishing grids you like.
I did do some construction over your illustration. I want to say first I think a lot of the parts of this image are already working really well. I don't have any notes for you on color, texture, design, or your rendering, I think they're all solid. And the foreground elements are really nice, too.
I called out some stuff in the drawing with numbers.
Where I think the struggle is is in establishing a consistent ground plain. Right now we have two going on, the earth, shown in red as 1. and the treehouse in green, 2.
1713713658547-treehouse-in-the-woodsupdate-copy 1.jpg
Funny enough, if I look at ground plain 1 and ground plain 2 as their own spaces, the elements existing on each plain are believable in their respective ground plains. Did I make sense?
The bike and the wagon, 3 and 4 are working well with ground plain 1.
The boy and everything on the treehouse are working well in ground plain 2.
The dog (6) is a maybe? I drew a box to show how I interpreted the dog's existence. But the dog could be subjective.
Now the trick is to get the treehouse and the earth in the same plain of existence. Right now to me it reads as the tree house is on a slant. I hope that I illustrated how I'm seeing that in the construction lines well enough.
There is one small issue with the branches coming out of the left and right of the treehouse. I am getting the branches visually mixed up with the roots. I would recommend experimenting with making sure the tree roots and branches are distinct from each other. Maybe with size and value. The roots could also be going in and out of the ground more? I know you'll find a clever solution.
I did a couple little drawings to show how I would think about solving this illustration's puzzle. Yours will look much better lol.
1713713658547-treehouse-in-the-woodsupdate-copy 2.jpg
I would think about how tall you want the tree to be. The top (a.) is how tall I think you have the tree now. For this I tried making the tree taller, seen in (b.)
Now (c.) is my attempt at trying to figure out how this could look when viewed from above. It is a little rough, but I want to show that I am thinking about the shapes as solids and drawing though everything. I did cheat and put this more in an isometric perspective. But I hope the ideas still come across.
I think maybe the easiest solve for you would be to keep all of the objects in the image that are man-made I think they are all believable. I think if you stretch out the tree like my (c.) example, you could make this more solid. So I think it's really just redrawing the root area.
1713713658547-treehouse-in-the-woodsupdate-copy 3.jpg
As I was writing all that I thought it might be helpful to illustrate what I was suggesting. Oh boy, this is a real difficult angle lol. I tried adding some shadow and highlight to help sell the depth. I also wanted to have the treehouse's deck stand out from the roots and ground plain. I cut the hill a little and pushed back the silhouetted tree. I shrunk the dog, bike and wagon to help push them further from the viewer, I want it to sell that we're seeing this up high with the birds. I also warped the latter a little to make it look like it's going down.
I do think the image could use a little more space in front of the tree, but that all depends on the story you're trying to tell here. I hope this helps with the next image you work on and if you choose to take this one further, please take anything I did that you found helpful.