Missing after replacing spark plugs

If it a v8 then your firing order is
cylinder on left side valve is 1-3-5-7 (left-right) & right side is 2-4-6-8 (right-left) towards front of the car to rear. Firing order is : 1-8-4-3-6-5-7-2-

if is a v6 then the firing order is

firewall side of the engine will be
2 - 4 - 6

Front of the car Radiator side will be
1 - 3 - 5

This is with you standing in front of the car

And if memory serves firing order is 1-6-5-4-3-2

What size engine? Check the gap on the plugs as well. "pregapped" is not always right