DECU - You don't say if you are flight tech or cabin crew but, either way, you must follow the manuals. Know all your boxed items in the check list, it is mandatory memory stuff, follow up by reading all the notes in the expanded check list.
Engine fires require a fairly straight forward drill, cabin fires a little more complex as the drill sometimes depends on where abouts in the cabin the fire is. Once again, follow the check lists.
Golden rules for all check lists are to not rush them and for any action you take wait and watch to see what the reaction is as it can effect your subsequent drills.
Best of luck in the SIM.
BlueEagle - moderator.