Standing in front of the car with the hood ( bonnet?) open the #1 cylinder/coil is on your left closest to the front, then #2 and #3 as you move towards the rear. To your right hand side would be #4 near the front of the car, then #5 and #6 as you work your way toward the rear of the engine; "Bank 1" is on your left and "Bank 2" is on your right and the firing order is on the top of the valve cover right in front near the #1 cylinder
It is a Mercedes engine, they are all numbered the same no matter where in the world you are.