If you have been following the tune up procedures your distributor cap is already off, if not then unsnap the clips and remove it from the distributor. There is no need at this point to disconnect the spark plug wires.

Pull off the rotor button and look at the tip. Is it burned, pitted or corroded?

Inspect the points. The contacts should be perfectly parallel and their surfaces should be smooth and clean. If the points appear burned the culprit is most likely the condenser.

As part of a routine tune up you will replace the spark plugs, ignition points, rotor button and condenser. You should also inspect the distributor cap and spark plug wires and replace them when necessary.