I'm first going to give tips on lineart. Now, I am nowhere near a professional, but I'm going to share what I feel like I made mistakes on when I was not as good. Hope that makes since. Comment any questions or any more tips on lineart and I'll give you a shoutout. This is all my opinion.
Sharpie. If you are more of a traditional artist, rarely use sharpie. There are exceptions for if you are more experienced, and you're doing a challenge then you're probably okay. Sharpies can give blurry lines which don't look as nice. Plus for nibs (tip of marker) you have two options; big and blocky, or thin and flat. That barely gives any variation within the line width, even if you you add more layers it will take a long time for it to look smooth. An alternative to using sharpie is any old pen. I find that it works better than sharpie for two main reasons. One is that the tip is a lot thinner so you can get more details. Along with that is that the pen can sometimes dispense more ink to add a little more difference in the line width. The other reason why I prefer to use pen is because the lines are more crisp, they don't soak into the paper and grow out. If you do not understand what I mean by that, grab any old marker and draw on paper. You will most likely see (unless high quality alcohol markers it may be harder to see) little branch like lines that extend from the marker. You do not get this effect with a pen. Another small plus, is that if you're using cheap paper, even printer paper, it will not bleed thru. Personally I find gel pens the best, they run out of the ink a lot more efficient.
Line Variation. Like I had mentioned in the first tip, line variation can help improve your art. Even if it is just a little. It adds more depth and realism to the picture. If you look in real life, sometimes the tiny line on objects can become thinker because of either shadows, or what the object is. It also adds an element that pleases the eye. I like using three different ways of doing this, but you could certainly add them together. One ways is by using a brush tip marker. I've only used Prismacolors brush tips, they work well and last a while. Although, I've noticed the tip strands/fabric will split if abused. Another technique I like to use is if the line is a longer line, or an extremely curved line, I like to stop it at the point when my hand gets uncomfortable. After that I add a few dots or a line. The third way I add line variation is by lightly and quickly drawing on the paper with a pen. Then, with other lines, you can add more pressure.
Clean. Unless if it's just a doodle, or sketch you should clean up your lines. That includes guide lines, sketchy lines, and scribbles. Your artwork will look more professional, and look like you care. Just by cleaning those lines up, it will look like you put in much more effort than you think. To hold with making clean lines more accessible, make your underneath sketch light and simple. Don't drag your pencil deeply into the paper, then you will still see an imprint of the lines after you erase. That will look sloppy, and like you are not passionate in art. Even if you do care about art and want to be your very best, it will still look like you don't
Hope I helped! Comment if you have any critiques.
