Here are six tactics for troop movement to help you get more out of your armies in Civ 6.
Attack to heal. Getting to the next level will heal you 50 hit points.
When you have several units attacking one target, plan the order of attack so more units can get experience.
Plan all unit moves and attacks at the beginning of the turn before moving to ensure everybody gets to attack.
Move a unit part way before promoting if you want him to be somewhere else.
Move highly damaged units to neutral or friendly territory to heal.
If you're about to take an enemy city, plan which unit you want to end their turn in the city and try to plan attacks to get them the kill.
Watch the related video for more details on these tactics and more in Civilization 6.