The Authors Alliance is a nonprofit that advocates for authors, libraries, readers and scholars (I'm on their advisory board); they've done a ton of great work, notably a tool for authors to claim their copyrights back from publishers, even when the original contract specified that the rights were signed away "in perpetuity."
The latest Authors Alliance project is The Authors Alliance Guide to Understanding and Negotiating Book Publication Contracts, a free, open, indexed, searchable guide to contracts that explains standard clauses, gives tips on negotiating better deals, and helps with specific scenarios, like academic authors who want to ensure that their work can be used by scholars, researchers and educators.
The fourth in our series of educational handbooks, the guide identifies clauses that frequently appear in publishing contracts, explains in plain language what these terms (and typical variations) mean, and presents strategies for negotiating “author-friendly” versions of these clauses. When authors have more information about copyright and publication options for their works, they are better able to make and keep their works available in the ways they want.