Trouble starting '72 Valiant

Start by first trying to figure if it's fuel, ignition, or some other problem

How is the "tuneup" that is, when was the last time the ignition/ carb saw any attention? Ever run a compression test? What general shape is the engine?

Then buy yourself a spark tester and use a SOLID core coil wire to test spark while cranking the engine USING THE KEY. You should have a nice bright blue spark at least 3/8" long

If all this is OK, look at fuel. Before you ever try to start "next time" get a light if necessary, pull the air filter and look down the carb throat while you work the throttle. This requires "tricks" and care as the choke will close, so hold it open. You are looking to see if the accel pump immediately shoots a nice shot of fuel. IF NOT the carb has boiled/ leaked dry, so look for fuel pump/ vapor lock/ fuel boiling issues