If you are using a meter with an incident dome (white hemisphere), simply place the dome over the sensor, stand at the position of your subject (or in similar light), take a reading with the meter pointed at your camera position and you're done. This method averages all light hitting your subject from all sources and works best in even lighting. This is not as inconvenient as it sounds in practice, as you really only have to be in similar lighting, rather than actually at the subject position.
Or if you are metering directly (no dome) from the camera position, you can meter off a gray card placed in the scene (or something else of known reflective value, like the palm of your hand and open 2 stops). Or if you are dealing with a spot meter or another kind of meter that reads a narrow angle, you can read the light reflecting from darkest object that you want to hold detail, and stop down two stops (or three stops, depending). All of the above is subject to having known and repeatable developing methods, and will be more critical for transparencies than for negative film. Also, none of the above will work for macro or close-up work, unless you add exposure.
Hope this helps.
Ben Marks