What year is your car? Some carburated car needs to be primed first before it can start. Priming a carburated cars requires one deep push on the accelerator pedal just enough to deliver fuel in the intake manifold.
Fuel Injected cars older:
Is your car equipped with cold start valve?
Yes: While the motor is cold, open the hood, and have someone turn on the ignition without starting the car. Listen to a clicking sound from the cold start valve. If no sound, check your cold start valve or take it to the part store that can do the test.
Fuel Injected cars newer without cold start valve.
No: Make sure that your coolant is full or at least the coolant temperature sensor is touching the coolant.