Turn one?
Deployment?
(Yes).
As soon as you and your opponent start pulling out your models and setting them aside for the game.
This leads us to the LIST.
Based on the models/units/elements that you have selected to play in the game, that is going to be the focus of the tactics played modified by mission.
In looking at your opponent's models, what are they doing to do with them?
How do those models interact with the ruleset and what do they favor on the table top?
The list gives the story of how and what your opponent is going to play.
Each unit is going to have a goal on the table, and the primary question is this: can you destroy it on the table, and prevent it from contributing to mission objectives?
If you can't outright remove it, or require a good portion of your list to do it, a secondary option is to stall it out- surround it, defect it, or tie it up for a few turns.
Unlocking the narrative of the list is KEY. An example of a list narrative?
Playing my Saim-Hann Eldar army, I'm pulling out jetbikes, vypers, wave serpents, and fire prisms.
The primary attacking units are my jetbike seer council, vypers, and fire prisms- short and long range firepower to remove opposing models each turn.
What is your plan to stop that?
Can you stop that?
In support are my wave serpents filled with guardians and aspects.
They are going to zip around and plug any holes in the battlefield.
Jetbikes are there for mission objectives, fast and nimble.
What story does your list tell?