The short version
A party empties early for three reasons: nobody can see anyone, there is nowhere to put a drink down, and the music is either too loud to talk over or too quiet to dance to. Costumes are what people remember; lighting and layout are what make them stay.
Light decides the mood before anyone speaks
Overhead lighting flattens a room and makes everyone look tired. The fix is not darkness — a dark room empties faster than a bright one — but several small sources at different heights: a lamp on a side table, candle holders on the mantelpiece, something lit at floor level. Three to five points of light in a normal living room is about right.
That is the whole logic behind the pieces in Decorate the House: lit objects that sit at different heights rather than one bright thing in the middle. Warm tones read as welcoming; cold blue reads as clinical, which is useful for exactly one kind of party and wrong for the rest.
Costumes: the two-minute rule
A costume that takes more than two minutes to get into will not be worn again, and a costume that cannot be sat down in will come off before the food arrives. Full-body inflatables are the clearest example: brilliant for photographs, impossible for a three-hour evening at a table.
Makeup is the part people get wrong
Grease paint sets in about ten minutes and then stops transferring. Applied five minutes before guests arrive, it ends up on collars, cushions and glasses. Applied forty minutes before, it behaves. Setting powder is not optional on anything that touches fabric.
Removal matters as much. Oil-based remover, then a normal wash — soap alone on grease paint spreads it around the face and irritates the skin. A flannel that you do not mind losing is worth setting aside in advance.
What actually makes people stay
Somewhere to put a glass down within arm's reach of wherever people naturally stand. A second room, even a small one, that is quieter than the first. And food that can be eaten standing up, with one hand, without cutlery. Those three things do more for an evening than any single decoration.
Candles, and the figure worth knowing before lighting one
Candlelight does more for an evening than any other single decision about a room. It is also, measurably, the thing most likely to end it badly. The National Fire Protection Association records an annual average of 5,894 home structure fires in which the heat source was a candle, causing 63 deaths, 532 injuries and $286 million in property damage.
The mechanism is almost always the same: more than half of those fires began when something flammable was too close to the flame — furniture, curtains, paper, bedding or decorations. Not a knocked-over candle, but a stationary one with something near it.
That is worth knowing precisely because the fix keeps the atmosphere. Clear 30 cm around every flame and the category largely disappears; the light does not change. For the rest of the room, battery-lit pieces give the same low, moving light without the clearance problem, which matters most in the places you will not be watching once guests arrive.
Source: National Fire Protection Association, candle fires.