These are the best resources I've ever seen on how to study drawing. I've seen too many bad tutorials / books / courses and I hope I can help you avoid wasting time on those too.

Most important videos:

Krenz Cushart: (turn on subtitles)
https://youtu.be/kbKqIJcIUCw
https://youtu.be/dgjx6y6B_G8
https://youtu.be/594WhCme2pQ
(importance of accuracy and master copies)
(This is the best lecture series to show anyone who doubts that accurate drawing is important for people who want to draw from imagination.)

Dorian Iten Accuracy Exercises
Level 1: https://youtu.be/HMX3K3YMbd8
Level 2: https://youtu.be/ecJO1LnjXpA
Level 3: https://youtu.be/LPywXVsRKT0
Accuracy guide:https://dorianiten.gumroad.com/l/accuracy?layout=profile
Use code "DORIAN" to get it for free.
https://www.dorian-iten.com/wp-content/uploads/2023/07/AccuracyGuide-eBook-v02.pdf
(Amazing exercises for traditional observational skills. It's recommended to watch the extended explanation in Dorian's Accuracy Guide on his gumroad.)

Ethan Becker Dragging Art over Reference:
https://youtu.be/RXb-Y_kz2aU
(learning how to draw what you see accurately)
(This video is the same as Dorian Iten's exercises. I am including here to show you that even animation artists who primarily draw from imagination will benefit from this exercise.)
(I recommend studying manga you love, anime-still frames, and model sheets from setteidreams.net)

PROKO: https://youtu.be/1J7RQvKnWf4?t=629
(I timestamped it at the right time for you already)

Explanation:

Developing an accurate eye is the keystone and foundation to learning everything else. Your construction, anatomy, perspective, lighting, will all look like shit if you cannot observe properly. Drawing from imagination is really just drawing from memory, but if you memorize bad-looking shapes, you're literally crippling yourself. This is also the reason why permabegs with 10 years of experience never improve. They simply never update their visual library with beautiful looking shapes.

Conversely, when you do get good at observation, all doors are open to you. You will be surprised at how quickly you can pick up new skills related to drawing and painting once you have this down.

Do yourself a favor and practice eye-training exercises for at least 30 minutes a day, before you do the rest of your studies.

The Rest:

Glenn Vilppu:
https://www.bilibili.com/video/BV1Fr4y1q7nK?spm_id_from=333.788.videopod.episodes&p=2
(Fundamentals!)

Pere Lecoq:
https://artofmemory.com/pdf/The-Training-Of-The-Memory-In-Art.pdf
(The best book ever written on drawing fundamentals. In the 3rd chapter of this book, you will find a series of gradated exercises for drawing perfect squares, circles, etc. You can skip that, if you'd like, but I wouldn't. Use the copy + overlay technique on circles / squares, from Dorian Iten. When you get onto the head copies, also do the overlay technique, and overlay from memory, like Dorian Iten talked about in his gumroad accuracy guide.)
(This is the guy who trained Rodin and other French master sculptors, painters. These assholes could paint entire realistic scenes in soft diffused lighting with millions of figures and accurate historical props from memory. Totally nuts.)

David Finch Roadmap: (Nice, basic roadmap)
https://davidfinchart.com/where-to-start-and-where-to-go-from-there-a-roadmap-to-professional-quality-art/
(basic guide for construction and anatomy)
Corresponding videos:
https://youtu.be/DMmsydblf7s
https://youtu.be/5sUbnpserx0 <- This video is great
(You can replace Bridgman with TACO Anatomy, Jack Hamm, Morpho, anybody else you'd like)

David Finch Study Streams:
Frank Frazetta: https://youtu.be/ZqJ2h4Jw5nU
Claire Wendling: https://youtu.be/7ukExmlSRWU
Simon Bisley: https://youtu.be/Z2CZKX089w0
Travis Charest: https://youtu.be/ko7H8FGwks8
Carlos Pacheco: https://youtu.be/jFkqUtJ4mRM
Kevin Nowlan: https://youtu.be/ni30Hp72aeY
Joe Quesada: https://youtu.be/atXd2HbHYO8
Ryan Ottley: https://youtu.be/st31pTH3fFo
Frazetta Painting: https://youtu.be/aLAhVqh7qJQ
(Making master copies and drawing from memory)

Feng Zhu sketch studies:
Sketching 101: https://youtu.be/22XYoenU-0c
Just Draw!: https://youtu.be/WLqWX7onVmU
(importance of drawing from observation regularly)
(good introductory lectures for people who are new to art and don't know how to study.)

Jason Brubaker - memory drawing system
https://youtu.be/s_NuJIJ6wGY
https://youtu.be/G8e2DcN5kAo
https://youtu.be/S9Cx4pIjSvA
https://youtu.be/gkbQnBi_JqU
pdf: https://dreamco.com/pima/wp-content/uploads/2017/08/cognitive-drawing-202-sm.pdf
Jason's portfolio: https://www.artstation.com/jason_brubaker
(This guy is great, he did some phenomenal work for Kung Fu Panda)

Boichi:
Drawing Hands: https://youtu.be/47YQShyZPeA
(Great explanation on the importance of memory in art. Turn on subs.)

Naoki Saito
Observation (Fundamentals): https://youtu.be/lOQ_DnR4Erw
How to copy art: https://youtu.be/B5QetP4aa8w
Fastest way to improve: https://youtu.be/8jsZGeaWkhE

Mark's Drawing Tutorials:
https://www.youtube.com/@moatddtutorials/videos

Takahara Sato:
Art Routine to become a pro: https://youtu.be/m7Ecp5GKI54

This /asg/ guide is really good:
https://drive.google.com/file/d/1cK9q7oeFRE58MVaSgUql662iGqCXC8Ah/view
(importance of memory drawing)

KJG memory drawing:
https://youtu.be/yx6dbybn-rk
https://youtu.be/WKbQ4TPMkFc
https://youtu.be/-RFz2yFSBVc
(memory drawing and rotating objects from imagination)
Good KJG YT channel: https://www.youtube.com/@superani58
(the eng subs are quite bad, but with some effort you can understand it. For example, when the subs say "dictation", KJG is really saying "模写" which means copying, drawing what you see in front of you, etc.)

Dave Rapoza on applying studies from memory:
https://www.youtube.com/watch?v=m4tttsdhn8o&t=733s
(repetitively studying the same subject + memory drawing)
(For those who don't know, Dave Rapoza is a living master. Watching this is recommended.)

Based Jimmy Miracle:
https://youtu.be/fkRmBqC7qf0
https://youtu.be/ULzw4-CI3tE

Madame Cave's "Drawing from Memory"
https://mega.nz/file/5dNC1QhR#jxNqbfNxHdDtau2sRDAIX8cUBItXKMLd9CFKgwDXo0I
(Introduction was written by THE Eugene Delacroix)
(You can execute the same process digitally, by pasting ref image to canvas, instead of tracing on gauze.)

Arthur Guptill
https://archive.org/details/sketchingrenderi00guptuoft/page/n1/mode/2up
https://archive.org/details/a.l.guptill1935
(totally complete drawing programs, from beginner to professional)

Ron Lemen:
https://www.youtube.com/@RonLemen/videos
(several hour long traditional figure drawing lectures)

Animator Beast's gesture drawing practice
https://youtu.be/yHJXLdCVD18
https://youtu.be/7y99O3wm4Cg?t=6003
(gesture drawing with accuracy)
(Clip Studio Paint EX can handle this easily, just import an mp4 into the animation timeline.)

Kirk Shinmoto:
Master Copy: https://youtu.be/YVAtRojlCS8
Master Copy 2: https://youtu.be/cF2UtfFT7y8
Anatomy Books: https://youtu.be/9pAMqgJXcbw
(approaching master copies with construction)

Will Terrell on how to build a Visual Library:
https://youtu.be/pOK2sDLtu2Q

Josh Black's daily training routine:
https://youtu.be/ugiP3-32_9Y
https://youtu.be/hA9UP9ZoekI

Christophe Younge Painting tutorials
https://www.youtube.com/@christopheyoungart/videos

Natalie Nourigat's figure drawing advice
https://youtu.be/Fa9CLiGhWr4

Painting studies:
Color Studies: https://youtu.be/1d577v_XBKA
Quick color studies: https://youtu.be/CVGZf5EQQK4
Ahmed Aldoori: https://youtu.be/3YXTlF4hzaE
Noah Bradley: https://youtu.be/kQfF-P70V2Q
Simplify drawing and painting: https://www.youtube.com/@SIMPLIFYDrawingandPainting/videos
Paint Coach: https://www.youtube.com/@paintcoach/videos
Daily Studies: https://youtu.be/jtfojuYEMTc

Minimaru:
Hand & Feet practice: https://youtu.be/pDCL7s8JjDY
90 sec figures: https://youtu.be/d86hKJNehI8
Basic Proportions: https://youtu.be/avcygKfCoXQ
Basic Anatomy: https://www.youtube.com/playlist?list=PLMzSsN13py1hIz1Q-s49LWF-IkKna9Swv

Hide Channel:
Croquis: https://www.youtube.com/playlist?list=PLTY4AtphBe8NS7WFIMIhHIBJVk3xQvi-q
Recommended books: https://youtu.be/TBqEj3tKD6o
How to practice:
https://youtu.be/tMoubXBGloU
https://youtu.be/eCtLmBShSho
1st year: https://youtu.be/QgnLM73R8oM
(turn on cc. not all are translated, but draw along anyways!)

Manga Materials:
https://www.youtube.com/@mangamaterialsyoutube9454/videos

Jeff Watts on Memory Drawing:
https://youtu.be/-NIvZZ7x3dc?t=2715

qrbits course:
https://youtu.be/aMlTKtmczzM?t=754
(recommend watching all of it, but timestamped at the essential advice.)

Glenn Vilppu: Art School drawing game (done w/ friends)
https://youtu.be/c0z04ickKoY
(good ol Glenn)

Misc
(Everything below this is just miscellaneous stuff that's interesting. Not all of it is necessarily about how to make studies.)

Zapata Perspective: https://youtu.be/_9tcy2436iM
Jeff Watts on the time it takes to learn drawing: https://youtu.be/KX0MrnzBJ8M
PSG Art tutorial: http://androidarts.com/art_tut.htm
Dan Thompson: https://www.youtube.com/@danthompsonfineart/videos
Rad Sechrist: https://radhowto.blogspot.com/
Neg Illustration Recommended books: https://youtu.be/Wy_4g-jTkgY
Steve Huston YT Channel: https://www.youtube.com/@STEVEHUSTONdrawsfromlife/videos
Alexander Mackendrick, on filmmaking: https://www.youtube.com/playlist?list=PLuntSxVsd5TNh8KJJysrDZCV8cz-ptFXI
Luis Borrero, Renaissance Drawing: https://www.youtube.com/@LuisBorreroVisualArtist/videos
Pikat, how to improve at art: https://youtu.be/XeIR7P82aPU

Simon aka Teal Line guy's redlines:
https://imgur.com/gallery/8eHzD

Inkwell, art business advice: https://www.youtube.com/@Inkwell/videos
(extremely whitepilling advice for artists)

Morro's How to Improve playlist:
https://www.youtube.com/playlist?list=PLWlOdihvL2_9JkM6ycZVZXcIXyWWxZQ7b

Natalie Nourigat
Comics Advice:
https://homeiswheretheinternetis.blogspot.com/2015/04/advice-for-aspiring-comics-artists-14-18.html
Feature animation storyboarding advice:
https://homeiswheretheinternetis.blogspot.com/2017/09/animation.html

Joe Kubert mail order dvd course:
Pencilling: https://youtu.be/Zt_j70hzSrE
Inking: https://youtu.be/sDc1b5qNSNI

YenYen Animation lectures:
https://youtu.be/JUO3wrCnOFk
https://youtu.be/O84C_11MUXM

Saejinoh: Pain Process
https://archive.org/details/youtube-wRNj1h5tVG4
(Marine bootcamp style training. Not recommended for the weak of heart.)

Figure Drawing apps:
Gesture Drawing!: https://www.artstation.com/marketplace/p/k1Vq/gesturedrawing
Quickposes: https://quickposes.com/en/desktop-app
Posemaniacs: https://www.posemaniacs.com/tools/thirtyseconds

Animation reference:
https://setteidreams.net/settei/
https://www.sakugabooru.com/post

Misc 2d Animation resources:
https://docs.google.com/document/d/12MrFro6y2Gv9WV7j71KHVKDiBEpjueryaBnoTZJ3QhM/edit

Glenn Vilppu:
https://tv.creativetalentnetwork.com/axChannel.php?id=58
https://www.bilibili.com/video/BV145411A7CV/

Craig Mullins Sijun Posts
https://archive.org/details/CraigMullinsSijunPosts
Backup: https://mega.nz/file/FYUjxaoD#RRgLiceoublag5i-WAKeT_h1mQgzeYW6y77DuB6aBjY
(400+ pages of art advice from Craig Mullins, the Godfather of Digital Painting, from back when he shitposted on Internet Forums in the early 2000's.)

Art Senpai Advice:

If you need to download the images here, get the extension "Save as PNG" because for some reason HackMD only lets you save XML files

A redliner's advice

For the links in the above image, here's the thread: https://warosu.org/ic/thread/6809247#p6809772

Ecorche Anon's Advice:

/Mecha/ general op's advice

Tableguy's advice

Site: https://gvaat.com/blog/analyzing-capcoms-anatomy-guide-with-english-translation-part-1/

Velleity Art's advice

Slowpoke's advice

Note: Slowpoke has done over 2000 master copies!

Yoga Anon's advice

Measure more:

Proko Measuring:
https://youtu.be/tZtnKp4fAPk
https://youtu.be/1J7RQvKnWf4

Dorian Iten Accuracy Exercises
Level 1: https://youtu.be/HMX3K3YMbd8
Level 2: https://youtu.be/ecJO1LnjXpA
Level 3: https://youtu.be/LPywXVsRKT0

Pantsu Ripper's simple, but effective advice:

Redblobsenpai's Advice:

Hanameru's Advice:

Glenn Vilppu:
https://tv.creativetalentnetwork.com/axChannel.php?id=58
https://www.bilibili.com/video/BV145411A7CV/
https://www.bilibili.com/video/BV1V441157du/?spm_id_from=333.337.search-card.all.click

Steve Huston anon's advice:

(I recommend searching Steve Huston on bilibili.com. It doesn't have everything from him though.)

Copy what's beautiful:

Take the Coompill:

Booba-anon advice:

Moai-anon advice: