When does the *game* start?
At the start of most wargames, barring special scenarios or historical battles, your army is at its strongest. Your list has all the models you have selected and you haven’t taken any losses.
Momentum in the early game is vital, as each game turn after the first you will get weaker and weaker as you take losses, and models/units get removed.
Deployment is KEY with that momentum.
Based on terrain and the units in play, where can you deploy them at the start of the game so they can gain an advantage?
Look at the attributes of your models- speed, shooting ability, durability, special rules, and deploy them in places where they can more out and gain the most advantage on turn one in using these abilities.