I'm thinking of writing a few essays about Tactics in games. Specifically, the tactics of TF2, L4D2, and D&D. Of course, the tactics in these settings have some application to each other, and for any tactical situation in general.
If I were to summarize tactics for any given situation, I'd simply say, "focus on destroying the weakest target at any given time." It's like Jesus, in reverse. Of course, there's a lot of nuance to unpack in that seemingly simple sentence that I'll get to later.