Design Learning Resources

Hello everyone!
I’m an Illustrator looking to make my work more design heavy, but I don’t know much about design apart from what I’ve picked up here and there. I would love to hear recomendations on books, or sites, that would help me out with this.
Mostly what I’m looking for, are resources that tell me about design more oriented towards covers or posters, something that as an illustrator I can grasp more easily and implement into my work, not so much design on logos, for example. Something more…general. Like on composition regarding shapes, colors, and their arrangement. Stuff like that, maybe.
Although whatever you think woudl be useful to me is very welcome!

P.S
As an example, I’m a big fan of Gigi Cavanego, who studied comics, and design, and his work really shows this background and sets him apart from other artists.