The first difference I learned about shooting on Medium Format Film as opposed to shooting Digital, was the difference in over or under -exposing.
Most Digital photographers know that modern cameras (especially any full frame camera) holds detail in the shadows but loses all detail in the whites. This means, that it is better to slightly underexpose your image instead of accidentally overexposing it. A slightly underexposed image can be fairly easily salvaged in photoshop or lightroom later on and any details seemingly lost in the shadows can be pulled back out. However, an over exposed photograph cannot be "fixed" later on. the details in the whites of the image are forever lost.
This is not the same with film photography. Film is "light hungry". This means that a situation that would typically mean overexposure for digital (and later on throwing away the image) is PERFECT for film. In fact, an underexposed film image is usually garbage.
I spent so many years being careful to never overexpose an image, the switch was surprisingly difficult for me! Suddenly I was reminding myself constantly that anything less than slightly overexposed would produce a "muddy" image and fighting the fear than bright images would contain lost details!
When shooting film, think about rating your film at half (more on exactly what that means later) and also overexposing it by one to two stops.
And remember, in low light situations (such as a dark reception hall) your digital will be best and in bright light situations (such as a mountain top wedding ceremony with a brightly lit background) trust your film camera to handle the glaring sunlight like a champ!
Simply Put: Film is light hungry, and Digital loves shadows!