Don gave a good one, spark plug examination.
MarkC gave a good one, VATS.
My suggestions are:
Remove the ECU coolant sensor connector at the sensor, two wires. Use an ohmmeter to check resistance in both directions. One, check sensor, s/b @70*F 1Kohms, 32*F 10Kohms.
Two, check into ECU harness for continuity, at the harness connector, place ohmmeter to DIODE function, place each meter lead into a wire, Note resistance reading, swap test leads, note resistance reading, s/b 500-1K in one direction, 10K-20K in the other direction.
If both items check out okay, sensor & wire harness to ECU, then plug into the ECU harness connector a 10K-12K, 1/4 -1/2 watt resistor. Then try to start, The high resistance places the ECU into cold start, and provides more fuel.
If car is equipped with VATS, wait three minutes after initial starting and retry with same key.
If you have the original ECU, make sure the calmap chip is changed also.
How long has the car been sitting? Injectors may be varnished. Spray some starting fluid in the intake hose/line, If it starts, then you know the next job...