This thresd will cover the CTS.
I would not replace the o2 sensor or ignition control module which include the coil packs unless there was an error code that indicated there is a problem. The ignition control module can also be cleaned and then tested. 02 sensor=$80 ICM=$280
Follow the fuel lines to find the fuel filter. Mine is located on the drivers side half way down the fire wall. I have 148,000 miles and have never replaced the fuel filter. Luck I guess. I would replace the air filter after inspection. And check the serpentine belt for wear and cracking. Most important- is to change and check the oil levels, these cars tend to start burning oil as these motors age. Hope this helps.