I think you're doing well so far! You've clearly identified the clavicle, you've pointed out the vocal box area--which helps a great deal in defining the form.
I would make sure that you're really showing more of that sculptural knowledge and drawing from the inside out. So while in comics we end up with a pretty simplified drawing, you want to be mindful that you're drawing the outside form of the muscles around the neck, as well as the muscles that go towards the shoulders--they're all connected to eachother. Also there's so many muscles, that the neck is a bit thicker (we usually shrink that neck stylistically, but it's a beefy thing.
And, especially in girls and teens, necks will be sometimes skinny, but once you hit adulthood in your mid 20's-30's necks will become about as thick as your head (*but not always, some ladies have real skinny necks, and I like to make my necks pretty skinny and much longer than normal in my comics as a stylistic choice). Also, the bigger the muscles of your character, the more the neck.
the pink line there is to also reference that the head height is about the same width as the clavicle to the side of the shoulder. Arms sit about the same height of clavicles so strong shoulders will help make a neck also look stronger. (although I probs made the shoulders a little too high but eh, I'm not perfect)
the blue line I have there is like my favorite muscle line for helping define volume in the neck. It starts behind the ear, runs around the vocal box area, and then rests in the clavicle. Super handy. I don't always draw it, but sometimes it really helps to define form. Like Andrew Loomis does that a lot and is a good reference for necks stuff. (and for heads at funny angles just in general.)
So I'd practice necks by referring to artists who are well known for anatomy and muscles, and become familiar with all the muscles that are on that shoulderline.