Over the years legend and myths have built around Zhuge Liang (Kongming). Not much of his writings has survived. Some writings have been wrongly allocated to Zhuge Liang - either due to simply not knowing or even purposefully as fraud. However, a few of Kongmings original writings have survived.
The Taoist Canon features Works by and about the Loyal Lord of the Arms (Zhong-wuhou ji); a study of Zhuge Liang featuring his writings taken from collections of his essays, letters and poetry. The letters included are some sent as guidance and advice to his nephew and son.
Unfortunately only very few of the related works are available in English, thanks to Thomas Cleary though, we are able to list a few:
Thomas Cleary: Mastering the Art of War (Shambhala Library)
Thomas Cleary: The Illustrated Art of War
I also generally would like to recommend the following:
Robert Moss: Three Kingdoms: A Historical Novel: No. 1-4
Thomas Cleary: The Art of War