Put the food in one part of the room and the drinks in another, or spread the food and drinks out around the space, so that people have lots of excuses to move around the room.

Create as much circulation at your party as you can. People circulate more when standing than when sitting, so try to encourage standing for those who can

Couples often flake together. This changes the probability distribution of attendees considerably, and so your chance of losing a quorum in a small-group setting. Small-group couple-events (e.g. 3-4 couple dinner parties) are very hard to manage in a high-flake society, as a result.

A large party is more like an Everything Soup: you mainly need to avoid ingredients that ruin the flavor for everyone else; beyond that you can mostly throw in whatever

Co-host parties with someone you like a lot but who isn't in your exact social circle, so that your two friend-sets can intermingle.

In a small group, the quality of the experience will depend a lot on whether the various friends blend together well. Follow your instinct on this, even if your instinct feels rude. It’s

Parties are a public service, you’re doing people a favor by throwing them. Someone might meet their new best friend or future lover at your gathering. In the short term, lovely people may feel less lonely, and that's thanks to you.