D&D is strategic, not tactical.
TLDR: What you do before combat is more important than what you do during combat.
First a bit of defining, because many people use strategy and tactics interchangeably. That isn't entirely accurate, but it's not wrong either. Strategy is about the things that happen before a battle, such as choice of arms, supply lines, and mass troop movements. Tactics on the other hand are what happens during a battle, such as pincers maneuvers, feints, and high ground.
The default D&D battle field is akin to a basketball court. It is well lit, flat, and indoors. There are few obscuring details, and most of them are left up to the DM fiat. The two opposing sides basically line up and use special abilities at each other until one side has no more hit points.
The reason that D&D is strategic not tactical is due to the rules. There are few rules during combat about positioning, numbers, or terrain. There are lots of rules about how to build your character, and some of those options are less than optimal. So the emphasis in D&D is making interesting choices before the combat starts- what subclass you chose, what spells you currently have available, what equipment and magic items you are carrying.