Study anatomy. Go to live model drawing sessions. And draw, draw, draw.

Follow a drawing course like drawabox.com, then focus on anatomy. Find a good anatomy textbook and practice its examples a little every day. The fact that you’re passionate enough to do colouring and want to start a comic makes be believe you have the strength to nail down the fundamentals.

To be fair, I think this nails the Early 2000s Newgrounds Aesthetic perfectly.

Check out Udemy, they have regular sales every few months with classes as cheap as 15$. There are a few drawing courses that will teach you the fundamentals.

Other than that it’s lots of practice.