House parties, in the crowded, loud music and beer bong-playing sense of the term, are legal as long as there are no underage guests inside the house. House parties are "busted" by noise complaints by neighbours; minors drinking, buying or being around alcohol; or by overcrowding, which creates safety issues. The only way to lessen the risks is to make sure that underage guests don't make it into your house. Guarding the door and asking to see proper identification may seem uncool to many, but it comes with far less consequences than a criminal record.
Schedule the party for a Friday or Saturday night. While it is certain that a house party on any day of the week will bother your neighbours, it is more respectful to do so on Friday or Saturday as it decreases the chance of angering your neighbours to the point of calling the police. Never throw a house party during the week even if it is a school holiday as many people have to wake up early to get to work. Respecting your neighbours is the surest way to keep them from turning you in.
Advise your neighbours about the party. Even if they are unhappy about it, it shows decency on your part for letting them know what is in store so they are not shocked or at least have time to make plans for an evening out. Let them know the party's time and that there will be many cars parked along the street.
Prohibit minors from entering your house. Even if they don't drink, having children under the age of 18 in your house with others drinking will get you "busted." Warn guests that any one they bring who is under 18 will not be allowed in. You are the one who is responsible if a police officer discovers underage drinking in your home.
Appoint door guards. Though bouncers may seem extreme for a house party, they are the safest way to ensure that minors do not enter. Choose about four of your friends to be the appointed door guards and set up guards inside at all back or side doors to make sure they are exit-only. There should be two guards, or "welcomers" at the front door at all times; one man and one woman to avoid bias.
Check the identification of guests if necessary. It is not illegal to turn someone away from your own house if you suspect them to be under 18. For all unknown persons entering the party that look underage, ask to see their identification. Chances are they won't have fake identification on them as most people don't expect to show it at a house party. If you suspect they are underage and they cannot prove otherwise, tell them to go home. Having a cute girl at the party isn't worth a criminal record if the police show up.
Keep the party inside. Don't let the guests meander outside onto the lawn and into the street as it draws unwanted attention. Only allow guests outside if there is a high fenced garden. Crowded parties get very hot and damp thus increasing the chance of guests overheating and passing out. Set up fans to ventilate the rooms and keep the temperature down.
Designate one person, preferably the host, to remain sober during the whole party. It may seem like mood killer, but if the police show up to investigate -- which if the house is in a college town or a patrolled neighbourhood they are likely to -- then there needs to be someone sober enough to explain to them that the guests are all legal age. A sober individual must also be able to regularly patrol around the house to check on the noise level.
End the party at a reasonable time. If the party starts to get out of hand and there are too many guests and the door guard system has failed, end the party by shutting off the music. If fights break out, people pass out due to drunkenness or are sexually assaulted, the police must be called. Once you suspect there to be minors present, shut down the party immediately as you are automatically responsible. Urge the guests to migrate towards the nearest bar and tell them that there is no more alcohol left in the house.
Don't meddle with the law. Homeowners and hosts who are caught serving or selling alcohol to minors face severe fines and marks on their permanent records. Cooperate with the police fully even if you don't have minors at your house party. If the police show up due to a noise complaint, it is wise to follow their orders rather than risk penalty fines. Even unknowingly, you could be charged with a noise violation, selling alcohol without a permit and safety issues due to overcapacity. If they request you shut down the party, do it.