Generally speaking, it's easier to host more people when a party is held outdoors. But at some point, people will want to sit down. Get out all the chairs you've got, including old stools collecting dust in storage, folding chairs, wood benches, even a hammock, if you've got somewhere to fasten it. If you have low walls in your backyard, you can set out a few plaid fleece blankets to make them more comfy and add a pop of color. You can also find affordable items at Ikea or H&M Home. Otherwise, ask a neighbor you're close with to borrow what you need and offer to return the favor, of course.