Unused film hates heat and humidity. Refrigerate rolls you will use within months; freeze anything you are keeping for years. Let film warm up for 2-3 hours before opening to avoid condensation.
Exposed film: the latent image fades over time, so develop your shot rolls promptly.
Expired film is shootable, but expect lower effective speed, more base fog, and color shifts. The classic rule of thumb: add one stop of exposure for every decade past expiry. The unpredictability is part of the charm - but for important occasions, shoot in-date film.