Hey Eric, first off, welcome to the forums, nice to have new blood, so to speak
So, i took a look through your DA gallery, and i have a few bits of general advice and comments i can give you, then i'll get a little more specific with the sprite sheets you've shown
So first off, i wanna say you seem to have a solid base to work with, your animations seem fluid and nice, although they also seem heavily based on sonic animations, not a bad thing but i'll touch on this in a minute. Overall your colour choice isn't terrible too, i would recommend at this point looking into hue shifting and saturation/desaturation to give your colours more "oomph".
You definitely have a set style, which is fine, but don't be afraid to push out of that. Its great to establish your own style but dont get too locked into it, and i've noticed with some characters you draw you tend to go more in the direction of your own style as opposed to their personal qualities, for example, your Mario drawing has him very slim and tall, which makes him more of a red luigi. This is something i struggled with at first myself, but you'll find branching out will definitely improve your own style too and give it more variance
Also, don't be afraid to dive into adding more detail, and breaking your initial outlines. I would absolutely look into observational drawing and learn how to work from building blocks, tacking our pictures in 3d space and as parts as opposed to a whole, this should be your next main step imo.
As i say though, you have a good base and a fantastic drive to create, so you're moving in the right direction, this is just the part where you should push yourself and challenge yourself to start seeing some major improvements.
When it comes to these sheets, they're pretty basic so not much can be said, but i'll go with anything major i've noticed:
Sonic: Looks mostly good, the only major issue would be the tilted head in the flume, waiting, cling etc. frames, it looks like you may have used a rotate tool instead of built them yourself? The outlines are messy and it's very noticeable in this smooth, simplistic style. I would also recommend changing the background colours for readability, blue on purple isn't the best look.
Tails: These are pretty bang on, the eyes seem off to me though, they seem slightly small, but only after looking at sonic and seeing how big his eyes are, it may just be a sake of when they're next to eachother, without seeing the eyes larger i couldnt tell. Then going onto Fang, he is back to the large eyes, makes tails' eyes seem a bit off...
Fang: Fangs eyes seem to be looking to far forward, as in, out at me, they could benefit from looking more to the right(our right). They also seem possibly pillow shaded? I cant quite tell without zooming in. Otherwise i think my only other comment is, i think this is the first time i've seen Fang without a hat, feels weird... Not bad though ;P
Overall the sheets look pretty nice, i think the colour choices could stand to be improved a little but i think once you look into hue shifting you might see what i mean.
Its a good overall start though and i look forward to seeing something more detailed from you in the future and seeing how your skills come along
EDIT: Ah, one thing i forgot to bring up was the ball jump sprites, i'm not sure how well they will look animated but they look a little... off, not sure what it is about them but something i cant quite put my finger on...
