Here's a great lecture and 2D anim demo by James Baxter.
I generally tell students and aspiring artists wanting to break into the industry "never work for free!" However, there could be times an opportunity presents itself where the unique experience and circumstances of a job are worth the free labor investment. That's the dilemma. Cinematographer Brad Rushing offers some perspective on this topic from a live action point of view.
Check out this great interview with animator extraordinaire Daniel Zettl. We worked together on the same team at Riot Games. Daniel is a super talented animator and shares a lot of solid advice in this interview. Enjoy!
Avatar, Smaug and League of legends - Interview with Daniel Zettl