
A more technical and challenging book is "How to Draw" by Scott Robertson. That one is good if you want more technical theory understanding (plus the illustrations are amazing).
Books:
* Fun with a Pencil by Andrew Loomis (everything Loomis is great)
* Perspective made Easy by Norling
* Christopher Hart's books (friendly to beginners)
YouTube:
* Proko
* Alphonso Dunn
* moderndayjames
Websites:
* Drawabox
* Kazone
Podcast:
* Draftsmen (Marshall Vandruff is an excellent source of guidance)