Art Tutorials
For my mouse art tutorial I linked to a Twitter thread in the description, but Twitter's changed a lot since then. The thread is no longer visible if you don't have an account, and some links are broken, so I moved all the links here with updated notes.
Absolute Basics
Monika Zagrobelna's How to Draw
4-part beginner's series starting from the absolute most basic level: how to control your hand when you draw lines.
TamberElla's How to Learn to Draw ANYTHING
Long image-form tutorial on how to draw anything. Original DeviantArt link was deleted, so I'm hosting it on Tumblr as allowed by the author.
Monika Zagrobelna
Monika Zagrobelna's tutorials are largely how I learned how to draw. Her tutorials are very dense with information, but in total it essentially gives you a full art school education for free.
While her tutorials were primarily on Tuts+ at the time of the original thread, you can now check out her website for more tutorials: https://monikazagrobelna.com/
Forms
Light and Shadow
Composition
Shading
Compilations
Lackadaisy
Lackadaisy is a running comic (and now animated series!) with famously good art. The creator (Tracy Butler) was kind enough to put together a few tutorials on her website.
How to Draw
Construction Drawing
Other Tutorials (also has unrelated content)
Youtubers
Text tutorials can be difficult for some people to get through, so you can find video content here. Unfortunately, I haven't actually seen many of these Youtubers' videos, and it's been a long time so I can't formally vouch for them, but they are here for the sake of preserving the thread.
Mark Crilley
Aaron Blaise
Lavender Towne
Sycra
Other
Text tutorials can be difficult for some people to get through, so you can find video content here. Unfortunately, I haven't actually seen many of these Youtubers' videos, and it's been a long time so I can't formally vouch for them, but they are here for the sake of preserving the thread.
The Etherington Brothers
These guys post tutorials on Twitter literally every day. They're on very specific subjects, but they're very simple and easy to follow. While it wasn't in the original thread, I'll also be linking to their Blogspot if Twitter isn't preferred.
Adobe Alternatives
Adobe products are very expensive!! While this list is relatively old, many of the programs here should still be suitable. I will still recommend against Gimp due to its difficulty, though.
Yet Another Anthro Tutorial
A primarily furry-focused tutorial I received through the furry grapevine. However, it also has incredibly well-written information on fundamental subjects like drawing from reference, human anatomy, and using forms.