My favourite youtubers are:
- Sinix (anatomy, rendering, design theory, shape language)
- Marco Bucci (composition, fundamentals, but especially color theory (!!!))
- ModernDayJames (draftsmanship, perspective, constructions)
- Ethan Becker (charisma, cutting out the bullshit, improving your art)
- Proko (all-around, but especially anatomy drawing)
I tend to stick to these for the most part, as well as watching some commented time-lapses of pros doing their drawings.
If you look up that top 5 and explore their free resources, you have a complete art education at your fingertips!