A pool changes the character of an event completely, and mostly for the better. It also introduces a set of problems that do not exist at any other kind of gathering, and the difference between a great pool party and a chaotic one comes down to a handful of decisions made in advance.
Start with the thing nobody wants to discuss: safety. Water and alcohol together is the one genuine risk at a private event. It does not require a lecture or a lifeguard, but it does require that somebody is paying attention, and that somebody should be sober. Designate that person before the day and make sure they know. It also helps to have a clear rule about the deep end after dark, when visibility drops and judgement is already softer.
Lighting around the water matters for the same reason and https://telegra.ph for a second one, which is that it looks extraordinary. Underwater lights or floating lights turn an ordinary pool into the centrepiece of the whole evening. If neither is available, positioning a couple of lamps so the water surface catches them achieves something similar. What you want to avoid is a dark pool in a lit garden, which is both hazardous and visually dead.
The practical logistics.
Towels. More than you think, and somewhere obvious to put wet ones. Without a designated spot, wet towels end up on furniture.
Changing space. People will want to change, and one bathroom serving the whole event does not work. A bedroom with a clear rule about it being the changing room solves this.
Floor. Water gets everywhere. Any route from the pool to the house needs a mat or it becomes a hazard, particularly on tile.
Electronics. Speakers, phones, lighting near water. Keep everything at a distance and use battery powered where possible. A speaker knocked into a pool is a bad evening.
Glass. This is the rule every experienced host follows: nothing glass near the water. Broken glass at the bottom of a pool means draining it. Plastic or metal cups for the poolside area, glass only at the table if you want it.
Food works differently at a pool party. People graze rather than sit down for a meal, they are in and out of the water, and anything requiring cutlery and full attention goes uneaten. Things people can pick up with one hand while standing work. Anything that spoils in heat does not.
Timing. Afternoon into evening is the natural shape. People swim while it is warm, then dry off as the sun drops and the evening shifts toward food and music. This means your event has two distinct halves and each needs its own plan. The transition around sunset is worth thinking about, because that is when people get cold, want food, and the mood either lifts or collapses.
Temperature after dark catches people out. Wet skin plus evening air equals cold guests, and cold guests leave. Have somewhere warm to move to, or heaters, or at minimum plenty of dry towels.
Numbers. A pool holds fewer people comfortably than the garden around it. If more than a third of your guests want to be in the water at once, you have too many guests for the pool. Nobody enjoys swimming in a crowd.
And music. Outdoors and near water, sound disperses fast and you will be tempted to push the volume. Resist it, because outdoor sound travels to neighbours far more efficiently than indoor sound does, and a pool party is already the kind of event people notice.