Nice art. The clop’s fine too. The muzzle looks a bit offcenter if you wanted to fix anything, the nostrils could move a bit, where they shouldn’t be is obvious if you look at the line across her eyes and then connect the nostrils. I see areas you could use rim lighting and ambient occlusion, but the two tone and gradients look alright, this was a simple piece.
 
It’s a bit of a misconception thinking that you need to make images increasingly complex to learn, because that’s only true if you want to learn complex things. If you draw a lot of pony muzzles you learn all the angles, you’re going to get more practice in than spending hours on a drawing which ends up being shading practice you already know - and I’m talking about myself here when it comes to muzzles, the nose on this only reminded me.
 
I’d say the weak points in your drawings right now are anatomical. The Trixie has a crease in her back like a human does, from what I see. It’s not that pronounced on horses. Another thing particularly here is the ellipse used on the back leg, it goes up way too far and curves too far back - usually it’s more of an ellipse and less of a C. And below that the sticky out bit of her ankle/hock is too stylized, it looks like there’s no tibia. I would tone down how angular that was and maybe even change the position of the leg. To not pile critique comments on every image, the ears on the Luna look like they are off center to go with the hat, instead of it affecting them.