FAERIE FOLKLORE RESEARCH
I get asked a lot for information on faerie folklore, so here are some places to start. And, as with all research, if you look at the primary sources noted in the backs of those books, you will find more material.
For a general outline of faerie society and a good starting place, Mika Loponen wrote an interesting paper that includes a discussion on the various names for faeries, general types of faeries, faerie gentry, and faerie mortality.
Another good place to start would be D.L. Ashliman’s page of changeling legends from the British isles
Also really useful is this Traditional Ballad Index. Tam Lin is there, along with many other fairy ballads. Of particular use are the Child Ballads.
For primary sources and good secondary sources, there are a lot of great books downloadable from the Internet Sacred Text Archive. Some of my favorites are Fairy and Folk Tales of the Irish Peasantry edited by William Butler Yeats, The Secret Commonwealth of Elves, Fauns, and Fairies by Robert Kirk, and The Fairy-Faith in Celtic Countries by W. Y. Evans-Wentz.
CONS AND HEIST RESEARCH
In reading and researching for The Curse Workers series, I realized how common cons and heists are in movies and books. Not only was researching helpful these helpful for that series, but knowing how cons worked turned out to be helpful for plotting in general. And, far and away, the most helpful book was The Big Con: The Story of the Confidence Man. The other one which was incredibly helpful was Influence: The Psychology of Persuasion. And the book that inspired me to write about con men in the first place was the true crime book, Son of a Grifter: The Twisted Tale of Sante and Kenny Kimes, the Most Notorious Con Artists in America.
I also really enjoyed Tokyo Vice: An American Reporter on the Police Beat in Japan for insight into criminals and criminal organizations.
While I mostly looked at vampire novels when I was writing The Coldest Girl in Coldtown, the two books I found most helpful in terms of vampire folklore/myth were Montague Summer’s Vampires and Vampirism (this is in print and also available as an ebook) and, although it is about how real bodies decompose, Paul Barber’s Vampires, Burial and Death was super helpful and interesting.
A good wilderness first aid book (the one I have is out of print, but there are lots of others) is incredibly useful to any writer of fantasy.