First you have to find out if it's all cylinders that are misfiring or only one. If it's all cylinders, start by checking the fuel system. If it's one cylinder, check that cylinder for spark, if no spark fix problem. Check cylinder for fuel, maybe as simple as it was for me, run car for a second or two, pull plug and smell for gas. If no fuel check injector, if okay, check wires to injector. One should be constant 12V while key in run, the other pulses to ground while engine cranking or running. If no 12V, check wires, if no ground pulse then check wires. All wires okay, check computer.
As some may remember, I just went through this with my Monte. Turned out to be a corroded lead for one of the injector drivers in the PCM. But I easily connected my car to the laptop, found that cylinder number 5 was misfiring.
Steve