Okay. But I feel like the negative space thing could still be seen through just the outlines, just in reverse, and a better way to learn is to try making art without lines.
Honestly, and I know this goes against what a lot of people are saying, I don't think you necessarily have to go through all of traditional drawing training to be good at drawing anything. Now, that does depend on what you want to draw, like if you want to draw almost perfectly realistic or semi realistic people it would be helpful to learn how to draw the folds of fabric and measure facial proportions like would be taught in a still life class.
Personally, I've been drawing for quite a few years and have only started taking classes within the last year. I think that the still life classes certainly helped me, particularly with backgrounds, but I think I was able to find my style beforehand. The only thing I could say about your drawings right now is they feel like you don't have a specific style in mind so they don't look confident. But that's something only practice will fix. Experimenting until you find what you like to draw should come first in my mind. While knowing how to draw realistically is nice, if someone wants to draw very stylized, I don't think they absolutely need to know how to draw a still life first.
Just keep practicing. You could watch some how to draw comics, manga youtube tutorials, or speedpaints.
There are 4 simple things you can do to improve your art, things you don´t need
a course for:
-use reference
-try to draw with more dynamic lines
-try to make everything you draw 3 dimensional
-colors: every color you are using is 100% saturated, you can check that in your drawing
app, pick a color and just put the saturation to 30% instead of 100%
Draw the same picture you drew with the lady holding the 2 guns with a reference.
Choose an interesting pose. Not straight on, try a reference which already looks interesting
and dynamic. Put it next to your drawing or try the line of action to train that.
Then try to draw with shapes instead of drawing the outlines, that will take a while
to learn that but that´s something that will make your art look better in the long run
here is a good resource for women holding guns
Sorry, but in that gun girl drawing I made she’s propelling herself into the air with grappling hooks, something that none of these poses are of, so I don’t think any of these poses will work for me since they’re all on the ground and stuff.
Art is more of a mindset than anything. Learned that the hard way. Unfortunately, nobody's born with these skills. It takes dedication and patience and the right attitude before putting the pencil on a paper.
I did plenty of mistakes and one of them comparing others and also, it's better getting things done than getting things perfect. By the way, perfection does suck. Imperfections make the work better.
Whether you call yourself good, bad, better, worse, all that crap doesn't matter as long as you're working on it. What are you afraid of? Sucking? I suck, as well, but hey, that doesn't matter.
Let me share this that got me back to drawing and got my confidence back:
My art went from this:
to this:
In 17/18 years.
Unfortunately, it doesn't happen overnight and everyone of us have their insecurities but I found ways to channel them. Use more of your mind when working and less emotions... keep the emotions in check and be the one who's in control.
Do I still have work to do? Absolutely. Learn structure... anatomy... find tutorials... find references... shading and most importantly... do art for you and once you get feedback... take the things that YOU need and leave the ones that don't matter that much. Work on it every single day. It's okay to be a bit selfish as an artist. It's gonna be a bumpy ride and make most of it. Work with what you have right now and improve on it and worry about the other parts when you get there.
Even if you made mistakes, OWN IT! Be proud of it!!! "YEAH! I DID THAT! WHAT ABOUT IT???"
Toss the "I can't do it" mindset in the trash and put on "BRING IT ON!!! I'M FUCKING DOING IT!!! I'M GONNA KICK ASS, BABY!!!!"
Many have given you answers, to simply make art better you have to draw alot! Just draw a lot what you want to draw, look at real life to learn anatomy better, to find what you like and want in a style you can always save pictures of those artists you like and break it down to what you like with their styles, is a person drawing eyes a way you really like, study that, is someone else drawing lines a certain way, study that part etc and eventually what defines you will show.
But those things will change a lot as well, you wont just wake up the next day and suddenly have your defined art style, the more we learn the more our style changes/evolves 
So when aiming to just generally improve at drawing, one of the most helpful pieces of advice I've found is:
Learn to draw fast first.
So before you get bogged down in trying to make every piece look very finished, or fiddling with small details on a piece, first get into the habit of drawing lots of small sketches; try to make it a daily habit or at least a few times a week. Get a sketchbook or a big digital canvas and just fill it up with sketches of poses, faces, things you see, just anything at all. These sketches are just for you, so they don't need to be perfect; if you make a mistake, just try again, maybe with a different approach, or note what you want to do differently next time. Do timed challenges like "I need to draw this in 5 minutes" and see what you can do with a timer. This will push you to think about the entire shape of the thing you're drawing first and teach you which details and lines do the most heavy-lifting.
Maybe you could join in the "Sketch a day" thread on the forums to keep motivated (but sometimes the quality of some people's sketches might feel intimidating, and I understand that. No pressure!). Some people like to keep their sketches mostly private (like me), but pretty much every artist should do them, whether they show them or not, or keep them or throw them away.
Get some good art books too. I think the art book that taught me the most is "Drawn to Life" by Walt Stanchfield. It's all the lecture notes the legendary animator used to train the animators who sparked the Disney Rennaisance in the 80s and it's just packed with wise advice for cartoonists. Another one that's FREE because it's old that's dated in attitude but still probably the best anatomical drawing book is Figure Drawing For All Its Worth by Loomis.
Also, please enjoy my tutorial hoard that I've collected on Pinterest:
I leave you with words I wrote at 11pm one night a number of years ago that went viral and then people started selling it on mugs and things without my permission:
Yes, certainly. I think that still life practice really is only needed for artist with more realistic styles that want to get even better faster. I think you can figure out a lot of things on your own without a class and a lot of professional artist, particularly those making a career online, have never taken an art class. Depending on your style and how fast you want to improve, taking classes isn't necessary at all
Refs are suppose to help you understand how to pose a character if you are stuck. Sometimes you might not find a perfect match to what you want and you may have to piece things together. But also just understanding anatomy and how a form exists in a space can help.
This is small details that can make a big difference
If you are looking for more of a cartoony style, I recommend looking up character sheets for animated shows. Just because something may look simple, it can still be drawn in a way that holds weight.
Quick question, how long did that sketch take you to make? The one I made took about an hour at least, maybe 2, but I know you definitely did not spend that much time drawing this or you wouldn't have done it.
I don't remember, maybe a few minutes, like 3. It's a rough sketch so those are not suppose to take a long time.
This is sort of what you practice with gesture drawings, where it's more important to get the form and worry about the fine details later.
When I do lineart, that takes a bit longer to do. But I always work from a sketch so I know what I am doing.
If I could do it that quickly my comic would be close to over by now. I never had a second step, I'd just fill in the person shaped color block and that would be it. I even had copy/paste models of the heads at all angles so I could drop them into the scene and draw the face on it, and only 1 of the 4 main characters faces took any effort to draw.
You might find this thread useful. It shows some of the preplanning that people use when making their comics/art.
Imma go ahead and disagree with anyone who says you don't need to study realism if you don't want to draw realism. My art usually looks6 like7 this3 - but the only reason it looks cohesive is because I can also do8 this10. A style is basically your brain's filter on how you perceive and re-interpret reality. You can't apply that filter when you don't understand what the things you're trying to re-interpret look like and/or what they do.
Now there are certain... more advanced things in drawing realism that you don't necessarily need to know how to do well if your goal is to stop at a particular style, but knowing realism will ALWAYS translate to better stylization (I don't, for example, render things super well... I theoretically know how to do it, but due to injury problems I choose to not devote my limited drawing time to something so time-consuming. I get around it because my art is stylized and I essentially just hide my weakness inside something I'm better at, but I would absolutely produce better stylized art if I felt more confident in rendering real objects).
To get better at art, you will need to train yourself to think about the 3-dimensional shape of everything you're drawing. Life drawing, studying shapes, drawing "boring" objects allows you to study something that's a more simple shape and understand how the light and its environment interacts with this shape. Eventually you will be able to piece these shapes together into more interesting objects, and over time your brain will automatically break down everything you're drawing into simple shapes and re-assemble them into a cohesive whole that looks "right" even though everything about it is technically "wrong".
Art is kind of like any other skill - you have to do the boring, grindey, learning bits and actively think about what you're doing while you're doing the boring learning bits. It's tough and it's not a whole lot of fun. But the reward is being able to draw things and feel pleased about them. You don't have to throw yourself into the doldrums (although if you want better art FAST, this is how you do it). You can just start with simple, quick studies thrown in-between working on more "fun" projects. You can also throw in the studies into your fun projects (though I don't recommend it). Do a shape and a couple 2-3 minute gesture studies as warm-ups before you draw - and remember, you want to stay ACTIVELY engaged with your study and what you're doing, instead of allowing yourself to go on autopilot and hope to get this boring thing done quickly so that you can do something else.
The best advice one can receive. If you are really serious about improving your work then you must realize that improvement & changes will not happen overnight. Watch video tutorials, get books on anatomy, perspective, learn to draw more than just people as well...watch videos on coloring and try to improve at that as well.
But most of all...just draw. Don't put pressure on yourself to "improve by XXX deadline"; just draw because you want to get better. No timetables...