This is not a tutorial, but this is what I’ve in mind when I draw lips. The best idea is for you to look for references in real life, different races have certain features on their lips, but that doesn’t mean that any type of character can’t have mixed features, it depends of the character that you want to create.
The most notorious feature from the lips is the relation in size between upper-lower lip, but if you add more variables to it you can get many different lips. I draw my own lips doing funny things sometimes, that helps you see how a shape can change so much depending on perspective and expression.
Drawing the head and hands by Andrew Loomis has a nice part about lips that you might wanna check out as well.
Hope this help! and have in mind this is just the way I go when I draw them, it’s something I did quickly trying to be helpful, I hope I’m being helpful.
Please don’t use this to trace the lips or whatever, draw for yeeeeeeeears like everyone does, this is a tool that may help you, not a stock.
Thanks for asking! The storm came back and I can’t sleep so, this was fun =)