These are the primary works on wargaming. If you only read these you can’t go wrong.
Dunnigan, James F., Wargames Handbook, Third Edition: How to Play and Design Commercial and Professional Wargames, San Jose: Writers Club Press, 2000. Written by the Godfather of Wargaming, this is your basic “how to” guide to commercial AND professional wargame design. Admittedly a bit dated; read for the core concepts.
Perla, Peter P., The Art of Wargaming, Annapolis: Naval Institute Press, 1990. Written from the professional wargaming perspective, there is also useful history of wargaming included.
Sabin, Philip, Simulating War: Studying Conflict Through Simulation Games, London: Bloomsbury 2012, 2014. Sabin delivers a more modern, nuanced approach to
wargaming simulation games.
Feature image TACTICS II by Charles S. Roberts, Avalon Hill, 1958 (personal collection)