What's the best way to find a dead cylinder?

cruiser said
Having rough idling/driving issues. Suspect that the engine (1974 225 bone stock everything) is missing on one cylinder. So what's the best way to determine which cylinder isn't firing? How about pointing one of those fancy temperature guns at the exhaust manifold adjacent to the suspect cylinder while the engine is running. If it's cooler than the rest, this may indicate a dead cylinder. Any other ideas out there? Thanks, all!

The infrared temp gun works if you start a cold engine. The dead one will be much cooler and not warm as quickly. Eventually the heat works its way through the manifold iron. You can pull plug wires off and see which one has no effect on idle speed and roughness.
Pull the plugs and check for one that is probably black and possibly oil fouled. Then there is a compression test or cylinder leakdown test.