K. Tempest Bradford, The Cultural Appropriation Primer, Writing the Other, 2018.
Site
Writing the Other
Writing the Other: A Practical Approach, undated.
[link to book and workshops that include writing about asexual characters, diverse characters and narrative structure, includes links to YouTube video workshops.]
Writing with Color, dedicated to writing and resources centered on racial, ethnic and religious diversity
[There’s a great list of questions and answers, including such topics as “How to research your racially/ethnically diverse characters,” finding beta and Sensitivity readers and more.]