Hi @Shellac-Belly!
Oh yeah I do have some and thanks!
Nah it's just a lot of trial and error and observing how other artists do it. My paintings were really muddy too :') The biggest reason why my paintings were muddy was that I wasn't conscious/aware of my colour choices enough? :'D
But now that I'm taking my art studies more seriously, the information I got from watching art vids is starting to click in my head lol :'D. Wished I wasn't just lazy and start implementing those tips more.
Haha about the tips actually my friend just asked me about that too 
. If you don't mind I'll just post what I've just said to him below 
Aye thanks man! Yeah sure. I think colour picking alot of like artists works. You will start to see that their colours are not random but have a certain pattern in them. So I believe that they do know how to sequence their colours in some way. You can see in some speedpaints they will have colour palettes in photoshop open and for some artists, they will say how they pick colours and it's through a certain order in the photoshop colour wheel. So it's all very technical, you just have to compare the value and saturation numbers in photoshop, and you will notice how the colour patterns. This might not be for all artworks. I haven't compared enough HAHAHA
But my values still need work. You still have to eyeball and adjust for the prepicked colours cause you might have picked wrongly, so if you have to make certain colours lighter or darker or saturated just do it. π€ It just helps you so you won't stray too far from the set values and colour theme yeah.
End of convo.
I think I have examples in my above paintings. You can see that I wrote out the colour values and saturations of the colours I colour picked so you can try doing that too! Just have to keep trying to breakdown other artists works enough so you can see how it works. I never really did this because I wanted to be " original " but yeah just do it! 
Like that quote: You have to know the rules before you can break them :''')
Here's some videos too that I think will help with painting and some other tips I got:
- Knowing how light works on objects, the terminator, highlights
- Notice Value Changes/ transitions in light and dark. Here's a video where I got of that
: https://www.youtube.com/watch?v=Nuhd2TgAlPY&list=PLwbkBfXxH3HCu0wR_K3ncvb0ks4qwV9d3&index=14&t=0s. I think this is most important after you have established the basic lights and shadow areas of your painting. This is where your painting will really pop I feel. I think, in the beginning, I never took notice of this but in lights and shadows there are also differences in them. Like in shadows, there're terminators/ bounced light etc. and these will affect the values in the shadows and light have its own thing too. You can see it happening in these sphere
A phrase that helped me understand this well is the darkest light cannot be as dark as the lightest dark. Somewhere along those lines.
If you implement these it will help add more depth to your painting!
- Soft and Hard edges for lights and shadows *
- Knowing your the object your painting forms and PLANES* ARE IMPT. Like from the Asaro's head, I think that was a key part in helping me paint better. It helps you how to separate the value groups of the head easier
- Simplify Shadows and light in shapes and know where the light is hitting
- Brushes and your strokes are important! Test your brushes and make sure it gives you the results you want. I know there's a lot of videos out there that says it is not ABOUT THE BRUSH and I can tell you I think I spent so long painting and having a hard time getting the values that I wanted JUST CAUSE I STUCK WITH THE DEFAULT BRUSHES. It's really about the BRUSH so yeah just make sure your brushes settings work for you :'D.
-Paint in the contours of the object. If you have sloppy strokes, it will show.
-Paint Step by Step, don't jump to painting details too quickly. - I fall victim to this so much in the beginning and I still do sigh. Always try to fix the main problems like proportion, light and shadows etc.
- Limit Palette, decide the value range of your painting and what colours are needed before you paint. - The thing I realise if you were to pick paints as you go, you won't keep track of the colours are using and eventually, things will start going muddy. I think this helps minimise that the most! You will have an easier time trying other colours once you have the palette working.
Other tips:
There's a video where it says to have a good painting you just have to have 5 steps of values. I guess it's true from what I've gotten
-If you're using photoshop, I think one useful trick I learnt you can do to see your painting in grey value in realtime is to go Window> Arrange> New window. It will duplicate an identical canvas as the one you're working on. The useful thing about this is it keeps the settings in each canvas separate so you can go View> Proof Colours> Custom> Select Grey Dot 20% to see things in greyscale and just pop the window out and downscale it so you can see the greyscale of your painting.
-Try your best to replicate someone's painting you admire to the best of your ability/ photography. I think this helped me the most when I was starting to paint because it really forces you to think about how to prepare your painting so you can get the end result but it will take a long long time though. I spent almost 24 hrs on a painting.
or you can just get Naranbaatar head tutorials, I think he covers some concepts I stated above really well and you can see how it all comes together! It's really good not only for painting but for construction too which is important too if you want to paint well. You can also learn how to organise your drawing process more T u T.
Sorry if everything is all over the place, I just like to ramble without organising my thoughts well haha. I will try and organise better next time, I hope it is still helpful in some way :'D
