I agree with Kay about the timing, but you can still make plans in the meantime
Food and drinks - for the last few years, my neighborhood has been having a monthly cocktail/potluck party. Everyone brings a dish to share and everyone brings their own drinks, which they can choose to share or not. They generally have several seating areas inside and out - try to have places where guests can put down drinks while they eat. Make sure trash and recycling receptacles are available.
Personally, I like it when there's quiet but upbeat music; it sets the atmosphere and makes it feel more comfortable. Also, think about ways to provide soft lighting.
It helps to designate a friend to greet guests and show them where to put food and drinks, so you're free to do other things.
Encouraging guests to chat and mingle - since you know everyone, when you have the opportunity, introduce people who you know have interests in common - their research or field of study, sports, hobbies, etc. You can get them talking and then excuse yourself to "go say hi" to someone else.
Activities - not really needed at adult parties, imo, so this isn't something I'd spend a lot of time on. Corn hole seems to be pretty popular right now, so if you have the space, you could set that up. If people want to play, they will.
That's all I have off the top of my head