a shot in the dark

If you hear a loud party and then some gunshots, chances are that the partygoers are just letting off some steam. Gunshots followed by squealing tires would indicate a drive-by shooting. Also, consider what day it is - big holidays are also days for random gunfire. It's difficult to distinguish the type of gun used in a shooting incident unless you're an educated gun person, but if the occurrence is close enough, you should at least be able to distinguish between a small-caliber weapon and a large-caliber weapon. The main thing to remember is to call 911 every time you hear gunfire!