Do you hate drawing as much as me? Do you constantly seek ways to make your art look better without expending extra brainpower? Are you lazy as shit and love using anything you can to replace actual drawing skill? If that sounds like you, great! This topic was made for you!
I'm S.A., local shitposter extraordinare. When it comes to comics, I'm always finding ways to shamelessly cut down time while pretending to have an inkling of skill without actually having said skill. I'm here to teach you my ways of presenting a veneer of professionalism while pretending to give a fuck.
Disclaimer: I'm not an expert as you would imagine and none of this is set in stone. Art be crazy. Let your imagination run wild. I'm just sharing the way I do stuff.
Trick #1: Gradients
When I was younger I had a thing about gradients, the people I saw use them always made them look shitty but when I started following SR (previous illustrator for Ragnarok Online) suddenly gradients were sexy again. I have no idea why I didn't use them up until recently because it's so braindead easy to make things look good by licking your screen with the airbrush tool.
What gradients can help do is a) soften your art and b) create focus on an area (generally the character's face and upper torso) by applying a value gradient. (See DOTA2's character guide for more examples of value gradients and also other invaluable information about designing.) Basically the general rule of thumb is that you would use a light->dark gradient from top->bottom of a character because their face is usually the most important part of them. Less important parts have less contrast - see how the gradient at the bottom of her dress makes the shading less prominent? We don't care about the bottom of the dress, so the dark gradient makes it have less contrast.
Trick #2: Hard and soft shadows
This is something very simple. If you have ever observed a shadow, you understand that the farther an object's shadow is from it, the softer it will be.
See how sharp the man's shadow is at his feet, and it becomes blurred as it gets to the head? See how the shadow of the pole-like object near him is merely a very faint darkness on the stone? Utilizing soft and hard shadows makes your art look much better without really requiring much other than gauging how far away the object is and then drawing it accordingly across a surface (see the pic below where the angled shadow below her chin is not a perfect angle, it slightly curves where her thyroid is, showing depth that indeed the thyroid is sticking out). When you do this, it gives other objects depth and tricks your mind into thinking they are 3d and have volume.
Of course, like everything else on this list, this isn't a hard rule and this is under a general light. If you have an extremely hard light then your shadows will be much more hard and if you have a soft light then you will have soft shadows.
Trick #3: Shade with the atmosphere you have in mind
This one's a little tricky because it requires things called "intuition" and "colour theory." If you're anything like me, I absolutely cannot fathom things that aren't concrete, my brain literally cannot wrap itself around something that can't be explained in a precise logical manner, so trying to understand something that you can only get from practice drives me fucking nuts.
"But wait S.A!" you say, "I thought you said this was a guide for people who didn't know that shit and don't want to turn on their brain you lying son of a bitch!"
I know, I know, but if I had to go through like 20 different colour theory tutorials to actually understand anything because nothing made sense before then, I'm sure that you can understand this as well WITHOUT going through 20 different tutorials all explaining this poorly.
This panel I used a red colour as my shading because it is an afternoon scene outside. So it's a warm colour to fit into the very warm atmosphere of oranges and yellows.
If we change it to blue here, well it's a little strange looking isn't it? The cold blue shading doesn't work well being in an otherwise warm environment.
It is nighttime here so I shaded with blue to go with the cool atmosphere.
If we change it to purple, well it seems out of place, purple is a warmer colour and it doesn't feel right in a primarily blue setting.
I can't show this example because spoilers, but this one is more intuition based: I am shading the interior of a tavern at night. While I could use blue to show that it's nighttime, the inside of the tavern is supposed to be warm and welcoming, so instead I settled with purple shading because it's between the ultra cool blue and very warm red. Hopefully this makes sense for you and you can use the atmosphere that you are constructing in conjunction with your shading techniques.
Disclaimer again: these examples don't mean you CANT do this but you have to experiment to see how to make it work well.
Trick #4: Form a palette as you draw your comic
If you don't already, use a palette where you can eyedrop colours and, in the process, make your comic consistent and neat. This means that you aren't going to pull out a neon green in your comic that completely clashes with everything else for no reason. Some people are good at making contrasting colours look great together without looking like vomit - but otherwise, keep your colours relative to each other.
This is my palette and I generally try not to use colours outside of it. It's obviously a work in progress and I'm still figuring out what kind of colours I like to use, but that's a big part of art I guess.
So if you haven't already, start compiling a palette for easy colouring and a more unified look.
Trick #5: Keep a library of stock images
If anyone knows my comic my character is a girl who has a brooch of roses on her chest. And if anyone knows me you would also know that I fucking hated drawing those with a passion. Then it came to me - well why don't I just draw this shit in high res, then scale it down and re-use it continuously so I don't have to waste time drawing these fucking things?
Yes, perfect! This will save you a lot of time in drawing things repeatedly, and also helps with patterns. One of my characters wears a hanbok decorated with flowers. I drew the flowers in high res, and every time I'm finished colouring, I drag the flowers over to his clothes and warp/resize them accordingly. I never have to draw this shit because I only drew it once and thats' all I need.
You can also use this for things like plants, flowers, background decorations like pots, etc. You can save a lot of time by drawing these things in advance and then placing them in a scene without much effort other than scaling and shading accordingly.
BONUS TRICK #6: Lettering
All right, so this isn't related to your art. However, it is something that will improve your comic by 300% very easily.
I'm not entirely an asshole, and I can forgive an amateur's sincere attempt at babby's first art. What I absolutely refuse to forgive, however, is BAD LETTERING, a comic that looks like this:
Look at this fucking garbage. This is inexcusable. It's trash. You want to pretend you're professional, right? Well nothing screams more amateur then having lettering that looks like shit. The best part is you can solve this with a few easy steps, and unlike me you don't have to spend 6 entire chapters of your comic trying to figure out how to do it correctly. I'm going to lay it out for you here and now.
1) Get a good font for lettering. Don't use something that's bold or too thin. There are plenty of free fonts at Blambot that you can use that are professionally done by someone who did lettering for comic books. If you're using comic sans, please! stop!
2) Center the text in your fucking bubbles! I don't know why I have to say this but if you think the text above looks good left-justified I don't know what to say! Always ensure that your text is centered in a bubble.
3) Arrange your text in a diamond shape to fit allotted space.

See how my text goes from small line, long line, small line? Because it's fitting the space within the circle. You want to arrange your text to both look nice and fit the space. So place your text in the shape of a diamond when possible.
4) Place a margin between the bubble's edge and your text. In the shitty lettering example the text is disgustingly close to the edge of the bubble. Having some space between the text and the bubble lets it breathe and looks less cramped.
5) Read these tips and follow them: Lettering Mistakes 1 and Lettering Mistakes 2
If you're one of these people with horrendous lettering - don't be ashamed. The early lettering of my comic looked like this.
ew.
But just follow the stuff I said. I'm by no means an expert at lettering but I know shitty lettering when I see it. I'm still in the process of figuring out how the best way to letter is but don't get caught in the trap of having garbage lettering - when your lettering looks good, it makes your comic look much, much better.
In conclusion
I hope this was vaguely useful to anyone who wants to use minimal-effort tactics to improve their art. I can't think of any more tricks I use other than a plethora of photoshop brushes because I can't handdraw anything for shit so I'm going to end it here. If you have any other tricks you'd like to share feel free to do so.
In closing have this pic of me every time I'm supposed to be drawing my comic.