2) Michael Waters. Formerly known as John Hansen, this guy is the powerhouse of the young writer world. He ran Teens Can Write Too!, which I'm proud to have worked with for a time, and he's a very active and sincere voice in the writing community at large. Also, a friend of Ch1Con. :)
4) Shannon Hale. This prolific children's writer has been an incredible voice in the past year for girls in fiction, and in general has a lot of great thoughts to share about publishing and social justice. Plus, her children are hilarious.
5) J.K. Rowling. Queen of sass, queen of writing, queen.
6) Maureen Johnson. Besides just being a great, feminist YA author, Maureen is full of quirky humor. I love seeing what new cleverness her Twitter feed has every day, and I also really appreciate her sharing her experience as a spoonie (chronically ill person) like myself.
7) Victoria/V.E Schwab. Victoria is a high-quality fantasy author, adult and YA both, and something about her Twitter just comes off as so real and human. I love hearing about her experiences as an author, which help show that even the best have to put in a lot of work to get things done.
8) Maggie Stiefvater. Maggie continues to be a force of nature in the YA world, and she just has so much personality. Her feed is always quirky and fierce. Queen #2.
9) John Green. He's a famous YA author and a force for social justice, particularly education. When he tweets, he's always got something valuable to say. Or, sometimes, just funny. Also, he fangirls over J.K. Rowling and is bffs with Maureen.
10) WeNeedDiverseBooks. This organization is the center of kid lit's social justice movement, looking particularly at fair and diverse representation in fiction and in the publishing world. Vital information to have, good feed to follow. As a disabled rights activist, I also recommend Disability in Kid Lit, for information particularly on the disabled segment of the movement.