Evan answered a question like this for writing here
My best advice is to learn how to draw things that AREN'T sonic-related first.
1. Draw comics where a human is getting out of a car, unlocks their front door, drops their groceries, and has to pick them up. Draw a comic where a person is racing on a horse. Draw a fight scene between two people. Draw construction equipment working on a building. One thing about comics is you will almost always have to draw something you've never drawn before in a story!
2. Learn storytelling through composition in illustration AND comics (they are two different things!). Draw a LOT of backgrounds, learning how to draw things in perspective is vital in comics.
3. Learn gesture and anatomy in real people, then study how it gets applied or broken in cartooning, and study how different cartooning is in different countries to have versatile understanding (because sonic isn't anatomically real, nor is he rubberhose).
4. Have an easy to reach portfolio site and an easy to find email contact.
After developing a portfolio of illustrations and comics that aren't sonic, you will have an easier time handling the work and convincing editors you can do the work on time.
Keep posting art online, and if you're aiming for sonic, bear in mind you need to have samples closer to the official style Make sure to keep posting sonic fanart so that the editors will more likely notice you and reach out.
Best of luck!