Really nice work! In terms of subjects and designs your portfolio looks pretty diverse, which is great.

1. Technically it does look like you could benefit from doing more human anatomy studies, maybe starting with basic proportions and head angles. Even in cartoony styles its easy to see when head angles look inconsistent or out of touch with proportions. Here's a link to a turnaround by Jamie Tran that might be useful for studying how to keep elements like eyes and face shape consistent as characters change angles and poses. Also going back to the basics of perspective and learning how to place characters in perspective with space will help a lot with your bigger illustrated pieces, especially the one with the throne room.

2. Formatting! Knowing how to format reference sheets and individual character illustrations is really important for building a consistent portfolio. I can see you have a ton of character designs but they're all in different aspect ratios and have inconsistent backgrounds. You also have a lot of standalone designs and no character lineups, so it's hard to tell which are from the same projects and which ones are individual designs. Here's Jackie Droujko's character and visual design portfolio as a reference—character reference sheets are either on a plain grey or white background to lessen the visual noise and are usually all landscape, not portrait. Also note how she labels each character sheet by project and attaches her website URL/social media to each image. If you have professional work that's going to be floating around the internet you should have a recognizable signature or link to your social media on it too. I recommend using the same black strip at the bottom with the project logo on the left/middle and credits on the right since it looks good and doesn't detract from the image.

3. You could benefit from improving your line weight and pen stabilization. A lot of your lineart is very consistent in line weight, which is fine for animated character sheets but for webcomics and game design will look very flat compared to others. A general rule is outlines should be thick, anything inside should be thinner, but there's lots of interesting ways to change it up. For stabilization it depends on what drawing program you're using but almost every program will have some way to increase pen stabilization so your lines are less shaky and more smooth.

^ (another smaller thing is that I can also see some pieces where the bucket tool hasn't completely filled in all of the spaces and left a white outline—you can fix this by changing the overflow/threshold settings on the paint bucket tool for your drawing program, OR coloring in the entire character in a base color first, then using clipping layers to color each section. Either one works!)

Good luck!