So who goes first?
In roleplaying games, the answer to this question is usually determined by initiative. The initiative order lists which character - be they one of the player's heroes or one of the Game Master's villains - is allowed to act first, then second, and so on until everyone engaged in the combat has taken an action.
ICONS is a very fast and loose "rules lite" roleplaying game, and the question of initiative (who goes first) is handled in that same spirit. Whoever initiates the conflict - be they hero or villain - goes first. So if the heroes attack first, each of the players take an action for their character (usually by going around the game table in order), and when they have each acted the Game Master describes each of the actions taken by the villain(s), henchmen, or other adversaries (or at least the ones still standing), resolving each in order.
Aside: I should probably note that ICONS is a little different than a typical tabletop roleplaying game in that only the players roll dice and not the Game Master. So the player rolls dice for their hero to attack. Likewise, if a villain attacks a hero, then the player rolls dice for their hero to defend him or herself from that attack, so even though it is the villain's turn to act, the player is always the one rolling dice.
This process continues until the situation is resolved, for good or ill. Sometimes the heroes go first, sometimes the villains. Everything is assumed to be happening at about the same time. If for some reason you need to know who gets there first (e.g. the hero and villain are both grabbing for the same object), you make a Coordination test with a difficulty equal to the opposing character's Coordination.
This simple approach works just fine, but sometimes you may want a more detailed, "realistic" approach to determining initiative order, since going first means someone on the opposing side might not get to take an action at all if you take them down in your first action. For important combats in my games, I make a list based on the Coordination scores (modified by their Acrobatics specialty, if they have it) of the heroes and villains, and the character with the highest Coordination gets to go first, and then we work down the list until the character with the lowest Coordination gets to act. This (usually) results in some degree of alternating between hero and villain actions. If a hero and a villain have the same Coordination score, the player makes a Coordination test against villain's Coordination to determine who goes first. If two players have the same Coordination, I usually let them decide who gets to go first - "after you, good sir!" - when their turn comes up. As before, the process continues until the combat is finished.
Sometimes, I'll shake it up a bit. Depending on the situation (like an ambush or surprise attack), I may let a player use their Awareness (if it is higher) instead of Coordination to determine their place in the initiative order. I may even let them spend a point of Determination to modify their Coordination by a specialty other than Acrobatics if they can justify its use in that particular situation - Athletics, Drive, Martial Arts, Pilot, and Stealth are the usual suspects.
So at my gaming table, that's how we (ahem) roll!
Thanks for reading!