I always check whatever is easiest to check first. and then progress to the other possible causes.
1) With the key on, check for voltage where the ignition wire attaches to the coil. If no voltage, test ignition switch/wires.
2) With the key on and the points closed, manually open the points by hand and look for a spark between the points.
3) If no spark/weak spark between the points, clean the points by pulling very fine Emory cloth through the points, followed by pulling a clean business card through the points to remove grit/debris. (Even if the points are new!)
4) If you don't have spark at the points by now, you need to check the condition of the wire between the coil and distributor. If that is good you probably need a coil.
5) Check the top of the rotor to make sure that the metal clip reaches the contact on the bottom side of the cap.
6) Check for spark at spark plug while cranking engine.
