Invite more people than you think you need / can accommodate. Many won't be available, and many will drop out at the last minute. Parties feel way more lively when there are slightly more people than can comfortably fit in the space.
Have background music on. You could create a playlist in advance or use existing ones online. You could even have a collaborative one that people contribute to in advance or on the fly.
Tell people in advance what to expect - is it a small, chill gathering where most people know each other? Or will it be large and lively with dancing? What should they wear? What should they bring? What food are you providing - should they eat beforehand?
It's a good idea to provide at least some food in the form of snacks. Try to accommodate a variety of diets. Examples of good snack choices are:
- Hummus/dips with veggies
- Crisps/chips and dips
- Cheese and pineapple sticks
Ask people to bring a bottle (whatever they want to drink). It's so much easier than trying to accommodate everyone's preferences - plus people like to feel like they are contributing something.
Having said that, have some basic backup drinks: Water, juice, tea, coffee, wine, beer, soda (diet and regular), maybe some spirits. The last thing you want is for drinks to run out.
Acquire loads of cups.
Create ambient lighting. No bright lights - ideally lamps and fairly lights.
Create zones. Note:
- People will gather standing up in the kitchen
- If possible, have a loud, dancing area as well as quieter spaces for conversations - make sure the latter has lots of cosy seating options
- If you have outdoor space and the weather is nice, use it!
- If you have a big enough space, consider playing different music in different areas to create a variety of vibes
Have plenty of obvious places for people to put their trash.
Expect to spend the next day cleaning, no matter how well behaved your friends are. People generate mess.