I've already shared a bunch over on the Drawpile, but I'll write down some of it for this thread.
Here is a bit of advice I would've given myself back a couple years ago.
0. Focus on yourself. I mean don't look too much at other peoples work and get discouraged (You don't know what their life is like. You don't know how much time and effort they've invested into their art.). You are you, and your art is unique. Simply focus on becoming a better version of your past self. If you strive to be like another artist, you will always be a second hand version of that artist. This thought makes me sad. An artist, who never really explored his personal art style.
1. Just stick with it. Eventually you will get there. Everyone else who hasn't reached his art goals has just simply given up prematurely. You don't need to draw every day. (You would probably make faster progress, but if you just can't get yourself to draw, then don't force it.) I've taken many breaks of several months. But I eventually always get back to drawing and painting.
2. Don't post your art online. Or at the very least don't make it a priority.
I say this, because you will naturally start to question every stroke you make.
"Will others like it?"
"Is that too lews for that board/community?"
"Why bother, someone already posted a better version of this."
"I can't post that online."
Just draw what you fucking like. Do it privately, so you can focus 100% on your idea and he process.
3. Practice deliberately. Don't "doodle around", or at least understand that "doodling around" will not help you develop as an artist. Because you're not adding new knowledge to your syste, but instead just do iterations on the things you already know.
Art is similar to math or any other science. You have to study a lot and practice a lot to get great.
It's funny how I've used to joing Discords back a few years ago, because I thought the streamer was great. A year or so later, they would still be at around the same skill level, while I've surpassed them. That's because I've a learning attitude. I'm open for everything. These streamers either have ego problems or are just plain lazy, and therefore stagnate.
4. Just copying images doesn't make you improve a lot. You should always have a clear intention with your studies. If your study goal is not clear, chances are you will not reach it. You don't need to do a perfect copy of something to capture its essence of it.
Ask yourself:
"Why am I studying this image?"
"What exactly am I focusing on? Color, Shapes, Anatomy, Composition?"
5.If you feel like you're having an "art block" or "don't know what to draw" just watch a documentary or learn something new.
Provided your process is not influenced by social pressures (as described in 2), you're probably just lacking some new input.
Art is shaped by your experiences. If you're a boring person, your art will be boring. Travel, get complementary hobby, whatever.
6. Draw while not drawing.
How to draw from imagination? You have to actually conciously see and analyze the world around you. Always observer. Kim Jung Gi was two years in the military, where he couldn't draw. But he drew in his head. He observed and saved everything he saw in his brain. (Drawing is ultimately just materializing an image, you have in your mind.) Have a note book ready at home, or in your backpack. Whenever you see something interesting, take a note. Take notes about the colors of certain object, of how the gradient of the sky looks like, or whatever you find valuable for you art. Make a litle sketch to capture something of interest. Then later on refine it at home, or base a drawing on it, or encorporate it as an element into your drawing.
Remember one thing at a time. Analyse something and focus on remembering that one thing. Then add it to your drawings. Then try to remember another thing. Great pieces of art are just a reflection of someones knowledge and experience (and also his mood and psyche).
7. Dude there are a ton of fucking books on image boards, why the fuck did you not look there earlier?
Like... yeah. Holy shit are there many good PDFs on mega.nz. Use them. (But only choose a hand full of them to study over a prolonged period of time. You can read a book five time and still learn something new on the fifth read.)
8. It's all about dem values. Value, Brightness is the most important. Values are 90% of a picture. Color doesn't fucking matter. It's all about color relativity (and value relativity, but we assume you've mastered values.). Think in terms of "warmer" and "cooler". Just use whatever fucking color you feel like, it really doesn't matter. I'm serious. Just keep the light source consistent. Take the light sources color and just mix it into everyhing that's hit by it. If you want to make a rim light, take the light sources color and just press down harder with your stylus. Voila, a rim light.
9. Use your arm and shoulder. (And a smudge guard.) If you want to have smooth lines, use your ellbow and shoulder. Hold your fingers in place and fix your wrist. This is allows you to create perfectly smooth lines for anatomy and organic shapes, but also long straights for more man-made objects and structures.