I’m not a professional concept artist, but I work with it in a professional setting, so take this critique with mileage.
First thing first, I noticed you both drew the concept and also want to make a 3D model of it. In practice, that’s fine.
However, unless you’re aiming to apply for a generalist position, most art companies these days would rather hire someone who specializes in one job only. So either professional 3D Modeler or professional concept artist. And I stress this point a lot. Before I got hired, I too tried to be a “jack of all trades” guy but it actually did more harm when I was applying instead of doubling down on the role I’m in now.
As for your drawing itself, I would do lots of research and collect references. Assuming you want to go down the concept art path, it’s also nice to start doing drawings from many different angles and perspectives.
I’m being serious when I say you would make the life of 3D Modelers verrrrrrry happy if you can give us drawings that look and behave well in 3D. Many times I have gotten flat 2D drawings with no other angles, and they’re a complete nightmare to sculpt or bring into 3D.
You can take a look at this guy’s portfolio as an example of drawing 2D Characters but also showing the scale, weight, dimensions so 3D Artist have a perfect guide to work with.
https://www.artstation.com/artwork/8wn1Eq
Not to mention, a concept artist also needs to be well versed in the fundamentals. Demonstrate you know color theory, textures, material, how light behaves. Concept Art is a very important role because you would be the first person tasked with bringing an idea to life or give a previz of what someone is aiming for.
Or if you want to be a 3D professional artist, then I would recommend finding already existing concept art and making 3D Models very close to it. For example, if you’re applying to Nintendo, I’m willing to bet they would be impressed if you took one of their concept arts for the Zelda games and made a very modern and high detail version of it.
Of course, you don’t have to do Zelda or Nintendo if you don’t want to. I believe there are other games or movies similar to your style. Like Dark Souls? Or The Nightmare before Christmas? Or you can pick whatever is your favourite and make a portfolio piece out of it.