In the desperate hack and slay of close combat the advantage goes to the best and fastest warriors, or those who have gained the extra impetus of charging into combat that turn. To represent this, combatants strike blows in a strict order.
Troops who have charged that turn automatically strike first. Otherwise, all blows are struck in strict order of Initiative (I). Combatants with a higher Initiative strike first followed by those with a lower Initiative. This is important because if a model is slain before it has a chance to strike, it obviously cannot fight back. Striking first is a big advantage, which is why it is better to charge your enemy rather than allow him to charge you.
If opposing troops have the same Initiative then the side which won the combat in the previous turn may strike first. If this doesn't apply, you should roll a D6 and the player who scores highest goes first.
For example: A bunch of Orc Boar Riders charges a group of EIf Spearmen. The Elves have an Initiative of 6, while the Orcs only have Initiative 2. The Orcs strike first because they charged. Next turn, the Elves will go first because of their higher Initiative.