Combat Sequence

Make a group attribute check – if appropriate – for access to the ambush turn. All actions in the ambush turn occur simultaneously.
Everyone rolls INITIATIVE. This is simply an INTUITION check, although some characters may get bonuses from skills such as tactics. On a tie, compare AGILITY, and if still tied, simply have each roll 1d6 and the highest wins.
All combatants then act in order from highest INITIATIVE to lowest. Each character may take TWO actions unless otherwise noted; larger creatures may have more actions. An action is a move, an attack, or a regular action. You can move twice, or attack twice, or move and attack, or any other combination. Creatures with 3 actions take two actions on their turn and one action on their INITIATIVE count -10. Those with 4 or more actions take two actions on their turn and one action every 5 INITIATVE counts later up to their total number of actions.
Once everybody has acted, return to step 3 and repeat until the combat ends.

Turns

A turn represents a short but unspecified length of time measured in seconds. Most characters have two actions to use each turn, unless they have an ability which says otherwise, and some creatures have more. These actions can be spent to move, fight, or perform other tasks, and can be performed in any order. For example, a character might move and then fire his longbow, or vice versa.

Each character (unless otherwise noted gets) 2 actions, 1 free action, and 1 reaction per turn.

The Ambush Turn

Before a fight starts, combatants can attempt to get the jump on each other. In practical terms, that commonly involves one of two things: unexpectedly initiating combat, or ambushing an enemy from hiding. However, it can involve any participant-initiated strategy.

If nobody is attempting to ambush the other, or if all combatants encounter each other simultaneously and launch straight into combat, the ambush turn is skipped. Only use the ambush turn if one group is deliberately trying to get the jump on the other. From a PC point of view, the ambush turn can only be accessed if the party specifically attempts to do so before combat begins; once everybody realizes a fight is breaking out, the ambush turn is long past.

Getting an ambush requires a group check. Either the whole group succeeds, or none of them do. This check is opposed by the leader (or the lookout, or the otherwise most alert or perceptive) of the target group. As always with group checks, success requires more than half the participants to make a successful check.

Anybody trying to gain access to the ambush turn needs to win an opposed attribute check against the intended targets. This is usually an AGI (stealth) or CHA (bluff), but the GM should allow any reasonable plan from a player.

All actions that take place during the ambush turn take place simultaneously, and creatures with access to the ambush turn may take only one action during the ambush turn.