1998 Mercury Sable it cranks but it won't start.

First thing to do is check to see if you disconnected any wires, also did you notice that when taking off the oil filter or pan that you shorted out any wires? Check fuses and check for spark and fuel pressure, post back the findings.

Double check the battery connections make sure its clean and tight. Disconnect a sparkplug wire and ground it to the engine, while cranking it over look for spark-do you have it. If so check for fuel