Liability for hosts:
It's illegal to serve alcohol to anyone under the age of 21. Hosts can be held responsible for injuries that an intoxicated person causes or incurs at or after leaving a party.
The State of Michigan holds servers of alcohol liable for injuries caused by intoxicated individuals who consumed alcoholic beverages in a home, office or other establishment.
Having fun (while staying safe):
Make sure there are nonalcoholic beverages and non-salty food available. Let the main attraction of the party be something other than alcohol.
Be aware of what is happening at your party! Discourage excessive use of alcohol, such as competitive drinking games. Intervene if you see guests hurting themselves or others.
If you notice someone getting drunk and losing control, stop serving them alcohol. Offer a nonalcoholic beverage or food to divert attention from drinking.
Consider using sober monitors at your party. Wolverine Wellness offers free trainings -- see Workshops and Trainings for Alcohol and Other Drugs.
When the party's (almost) over:
Do not combine drinking with driving.
Encourage designated drivers (those who won't drink at all or who consume 1 or 2 drinks early on).
Intervene if you see someone intoxicated who wants to drive home. Take the keys away and offer an alternative way home (cab, bus, ride with a friend).