That study of the shape of the eye on the left is amazing. I would strongly recommend doing more of those, especially if you enjoy them. They can be tedious (I admit I should make more of those myself), but if you like them, actually understanding how a shape works in space is incredibly helpful for your growth.
The anatomy of the skulls could use more work, but you'll get there eventually if you keep practicing, so I wouldn't worry too much about it for now. I would actually recommend you work on your strokes instead. From your other drawings, it looks like you enjoy animation. You should take a look at how some animators tackle figure drawing, like Glen Keane, for example. You can see that he also goes several times over the same line sometimes; however, there is a flow to the lines that comes from how fast he draws them that I think you would benefit from. For example, if you look at the bottom right skull, there was an opportunity to make the top of the skull a single round line that I think would make it look a lot nicer.
There are also some bad habits that you can avoid if you have recently started drawing. For example, if you are currently drawing using your wrist, it is very helpful to try to use your whole arm or at least your forearm to draw. Not only does it make your lines nicer and give you more control over them, but it is also healthier for you since it will reduce your risk of getting carpal tunnel or similar joint problems.
That study of the shape of the eye on the left is amazing. I would strongly recommend doing more of those, especially if you enjoy them. They can be tedious (I admit I should make more of those myself), but if you like them, actually understanding how a shape works in space is incredibly helpful for your growth.
The anatomy of the skulls could use more work, but you'll get there eventually if you keep practicing, so I wouldn't worry too much about it for now. I would actually recommend you work on your strokes instead. From your other drawings, it looks like you enjoy animation. You should take a look at how some animators tackle figure drawing, like Glen Keane, for example. You can see that he also goes several times over the same line sometimes; however, there is a flow to the lines that comes from how fast he draws them that I think you would benefit from. For example, if you look at the bottom right skull, there was an opportunity to make the top of the skull a single round line that I think would make it look a lot nicer.
There are also some bad habits that you can avoid if you have recently started drawing. For example, if you are currently drawing using your wrist, it is very helpful to try to use your whole arm or at least your forearm to draw. Not only does it make your lines nicer and give you more control over them, but it is also healthier for you since it will reduce your risk of getting carpal tunnel or similar joint problems.
Hope that is helpful!