First of all: There is no obvious difference between working with a flash when doing digital or analogue photography. Eventually, the same lights and shadows are recorded and stored on some kind of media, be it a memory card or the film emulsion.
Both of the films you are mentioning are relatively tolerant to over- and underexposure, so using TTL exposure metering is your best bet. I am not sure what JoanneC is referring to in her second point, where she claims that flash metering is not working very well. TTL flash metering has been around for more than 30 years and actually, it works as expected. If you are using a modern lens with distance indicator (AF-D or newer), the flash metering will also consider the focus distance when calculating the estimated flash energy, so I can't think of a single situation where you are better off calculating the flash settings manually instead of letting the automatisms do their job.
One final issue is of course that with a film camera, you have no way to immediately check the results. Using a single shoe mount flash, you are however pretty limited anyway in how to direct the light. When using studio flashes (one or more stand-alone flashes) in the pre-digital area, most photographers used Polaroid (instant) cameras to check the light conditions.