You basically just get a screenshot of what you're tracing and scale it down. It's pretty simple
In particular, I use the PC game and I record Sonic in Station Square at the beginning of the game from all directions and all of his animations (that you can see from the hub worlds, so basically just running, jumping and spin dashing). For consistency, I use the free camera and keep that pointing as low as possible (holding the right analog stick down during jumping so it doesn't shift up).
Then after that, I take a screenshot of the frame I want into GIMP, then I scale it down to where I feel Sonic's height should be in comparison to the original sprite, and I remember what percentage that was so that I can apply that to screenshots of all of the other frames of animations I took for him.
It's also important to make sure every animation frame in each direction is the same, so just make sure the feet and hands are consistent between the direction frames.
For scaling purposes, here's the standing front frame I used:
Just in case you want it to be consistent with mine.
I also ripped the standing frames from SRB2's Sonic from all angles for comparison so that I could emulate the style as closely as possible.
I'm also probably going to use SAMDL for other animations that are a bit harder to get. I could use Dolphin and the free look camera there, but it would be a bit more annoying I think, now that I figured out how to view the models and all of the animations in that program.