THE ART VAULT is a learning hub I have created a few years ago, it started as this Tumblr site where I would gather useful tips & tricks. Now it is a big art knowledge database and I still post there some of the best making of and tutorials from the greatest artists in the world. Quality over quantity is the rule.
To make it even more accessible I also created a Facebook group that is even more often updated because any member of the group can post inspirational material. Feel free to join and contribute!