A classic textbook about strategy is "The Art of War" by Sun Zhu. It's public domain and pretty short.
Another great books are "The 48 Laws of Power" and "The 33 Strategies of War".
For anything more complex, I recommend you to look into game theory.
If you want a pop sci introduction, Tom Schelling's Strategy of Conflict is great.
It won't help you do any better in strategy games, though.
A big part of the reason for that is that two player games we play for fun like Star Craft are inherently set up as zero sum games. From a game theory point of view, you just minimax and are done. (You might need some randomisation to be optimal.)
The really interesting parts of game theory are non-zero sum games.
See https://www.lesswrong.com/posts/tJQsxD34maYw2g5E4/thomas-c-s... for a review.