In my experience people err because they're afraid of not cooking it enough. So they either cook it over really high heat, overcooking the outside, busting open the sausage, or they kill it with too much moderate heat.
As we move into grilling season, and there's no better way to cook a sausage than over the smoky heat of live coals, I encourage you to grill sausages often. All carnivores around you will be happier.
How to Properly Grill a Sausage