Wide angle lens, aim at where you know or have a reasonable idea where the fireworks will appear in the sky. Bulb exposure at mid-aperture (f5.6) 30 seconds to capture several bursts, the longer exposure providing a huge number of 'trails'. ISO 200 to 400 film is good. It does not have to be perfect. Be it noted that the digital examples you see on the web are actually layers: several exposures superimposed, so too those of night skies.