Hello and welcome to pixelation! First I must say that both of these pixel arts have a good solid form, and that most of your troubles come from shading and coloring. For Orianna's head, the blink looks pretty alright. I don't know how a blink works for a robot; but for humans, when we blink and our eyes are closed, our eyelids are visible.
I noticed in both of these drawings, that your outlines will often times be double pixels on any turns or angles. Make sure your pixel brush setting on whatever art program you are using is at the lowest it will go for a cleaner outline.
Example coutesy of Sam Keddy.
For the deer head, First what you want to focus on is where your light source is coming from. It can be helpful to sometimes draw the light source and then later remove it. Studying reference pictures will help you too. For the below the eye sockets, it seems to be mostly composed of upper lines/ridges, with harsh shading underneath (that make's sense since the top of the ridge is at the same level of the skull, while the deepest part is sunken far to the back) Looking at the skull from a different angle will better show what I mean.
General shading on the skull helps better give the illusion that it has depth. Don't be afraid of darker colors!
A common mistake newer artists have is being afraid to shade out of their comfort zone (out of corners and into the middle of the drawing); but if you look in real life, only perfect circular/square objects have shading to the side. Anything that has form will have shading in more places than the corners.
For the antlers, it can be hard in pixel art to show textures since we can only use a certain number of colors and our "brush" is per pixel (instead of a normal digital brush that automatically can give texture and hues in one stroke). An easy way to combat this is to simplify and enlarge the texture. This is commonly used for bark in pixel art trees, pixel art fur, and I don't see why antlers couldn't be the same.
Lastly, don't forget to color shift. A skull has more beige and pinkish hues than yellow.
A rough side by side comparison of what I explained below:
