Setting a Party Order
Source GM Core pg. 43
In exploration mode, it often matters which characters are in the front or back of the party formation. Let the players decide among themselves where in the group their characters are while exploring. This order can determine who gets attacked first when enemies or traps threaten from various directions. It's up to you to determine who gets targeted based on the situation.
When you come out of exploration mode, the group usually remains in the same general formation. Decide the PCs' exact positions, with their input, if you're moving to a grid. If they come out of exploration mode on their own terms, they can move around as they see fit. For example, if they detect a trap and the operative starts attempting to disarm it, the other characters can move to whatever locations they think are safe.
When you come out of exploration mode, the group usually remains in the same general formation. Decide the PCs' exact positions, with their input, if you're moving to a grid. If they come out of exploration mode on their own terms, they can move around as they see fit. For example, if they detect a trap and the operative starts attempting to disarm it, the other characters can move to whatever locations they think are safe.