Things necessary for an engine to start:
1) fuel/ pressure
2) healthy spark
4) clear exhaust
5) correctly timed engine
1st step see if you hear the fuel pump come on when the key is turned on, If it does not sometimes you can kick the fuel tank to get it to work (this is for fuel injected cars with fuel pump in the tank btw) If that gets it working you will need a new pump
If it works great, if nothing makes noise, on some cars you can disconnect the intake hose and spray carb cleaner into the hose, this will act as a subsitute for gasoline. If the car fires you have a fuel delivery problem (pump/filter) you should check for power back to the pump before replacing.
If you have fuel, proceed to begin checking for a good healthy spark. if you have no spark work from the plug wires back.
since your car was recently a running car with no problems until it was parked I believe you have either a fuel or spark problem, I would concentrate on these two area first, my guess is its a fuel problem