I might be biased for some almost personal reasons, however I think there is one book that anyone serious about the field should just read, period.
“Trades, Quotes and Prices”
Authors:
Jean-Philippe Bouchaud, Capital Fund Management, Paris, Julius Bonart, University College London, Jonathan Donier, Capital Fund Management, Martin Gould, CFM - Imperial Institute of Quantitative Finance.
I’m a practitioner and this book is foundational.