My 2004 Cavalier will not start on first try but will on Second try?

That could be your fuel pump.If the check valve on the top isn't sealing it will let the fuel pressure bleed off the fuel rail.Then when you try to start it it just cranks over.When the fuel rail pressurizes again it will start and be ok til the car sits for too long again.Try an experiment.Turn the key(so the fuel pump will start) on but don't try to start it.Do that several times then crank it over and see if it starts right up.