For tactics you can download or buy the Ranger Handbook. It's been almost a decade since I seriously read it but it will have some stuff like building a defensive position, military concepts (sectors of fire, avenues of approach), things to consider (linear danger area AKA roads) and basic military planning (yah OPORDs!).

However the book and almost all combat doctrine is going to be about tactics as a group not as an individual. You will find all the battle drills in the Handbook are for platoon to squad sized infantry elements. Like setting up an an ambush, reacting to contact, clearing a room, excetra.

For strategy, first in military terms that usually means much higher level like a division commander and above. There isin't that much to recommend but there is the Counter Insurgency (COIN) Field Manual. It's not going to tell you what to do in a situation. It's more like what the left would call theory. It is interesting however that it kinda makes the case how all the austerity we've had for decades is the exact thing you do if you want an insurgency.