Basically, a bit of background: I pretty much grew up on shoujo manga art like Arina Tanemura, Hino Matsuri, Ema Tooyama, every other well-known shoujo artist out there, and mostly, Yoko Maki. Yoko Maki's still my idol, regardless of change in art style. But anyways, the fact is I grew up with shoujo stuff, as well as the usual manga style. So that's probably why my lineart is the way it is because it's how most manga is drawn in.
Also, my lineart is very messy. If you're working on a really big piece (I usually draw in 2000 by 3000, unless I'm drawing for something to be printed, then I use either 8.5 by 11, or 11 by 17, which sometimes screws up my laptop ugh), you don't need to be clean about it. If it's fairly small, you might want to but you don't have to. For me personally, I like to just let my hand draw whatever it wants, and not think about it much (as well as worry if this part is perfect or not, etc). In short, I let my imagination flow. That's probably how I am when I draw in general. It's fairly obvious when you look at those artists you idolize (most of mine are on pixiv tho lol).
Here are some examples of pixiv works that like to do this. You can choose not to, but if you ever want to do just lineart, playing with your line weight makes it look more interesting. Some people (I've seen a tutorial on DA I believe) will probably tell you to play with the line weight according to your lighting profile, ie heavier lines for shadows and lighter lines for those near the light source. I prefer not do it that way because A) I do my lighting profile later on when I've put the base colors, and B) I prefer to focus on just my lineart when I do it. It really depends on how you work, and what you're most comfortable with.
Second (or third? Idk anymore) is to add details. For me, I don't like to add a whole lot of details (such as drawing so many hair strands for the hair). There are times I might lessen it from usual, there are times I just go with what I think looks right. I'm still not sure which one would go better with how I color (and on a sidenote, I'm still trying to figure out how I want to color), so I can't tell you how much detail you should put, but if you're doing just lineart, adding details will make them look even better. I know it takes a while, but with lots of practice, you could do it in under an hour, or 30 minutes. Idk how long I take, probably less than 30 minutes tops, excluding all the changes and mostly just doing the lineart itself. But an example would be the Kagepro lineart I showed earlier on. I added details to his sleeves and collar, and it looks nice.
Another is, make your lineart curve as much as you want to. Doesn't mean you should just make squiggly lines lol. What I meant by that is, don't just draw a straight line, try and shake things up a bit. For example, the last pic, if you look at how I drew Shinoa's sleeves folding, you'll notice I curved down a bit, then jump back up, forming a really sharp indent in the lines... Reading that again, I'm pretty sure you guys are gonna get confused as to what the fuck I'm talking about. If someone is, please let me know. I'll try and see if I can circle some of these. But anyways, try and shake things up a bit. As I've mentioned on somebody's thread, curves are more interesting than boring lines. Dynamic poses are more interesting than just your sprite standing there. Doesn't mean you need to stray away from straight lines, but don't just make your whole lineart consist of straight lines. Look at how I drew her ribbon. Usually, people would just draw it with one curve. It's better to add some volume and variety to the lines by adding lumps into its form.
And I think that's all? If ever anyone wants to, I can probably post a video (if my shitty laptop can handle it) of me doing my lineart. And if someone is curious as to how I draw in general (like anything under the sun in terms of art), feel free to post.