Go around the outside
Minimising the amount of furniture in your space is a good start, but your guests will still need somewhere to sit and a table to rest their drinks. Arrange furniture around the outside of your area, leaving the middle free for people to mingle.
A small trolley is the perfect way to give you table space when you need it but can be easily moved out of the way when the serving is done. A long narrow rug on the deck elongates the space and draws guests away from the entry, preventing it from becoming too crowded.
Divide and conquer
Instead of having all your drinks and nibblies in a central place, set up multiple stations around your party space. If they’re all in one place, people tend to congregate around them, making the place feel more crowded. Having an even spread of guests in the small space will make it feel larger than it really is.
Select furniture that is not too big and chunky. A wire outdoor setting still gives guests a place to sit, but doesn’t take up as much space as say a timber seat. Bar tables are also a good idea. Because they are tall, they give the impression of more space than lower tables. People are more likely to stand around a bar table rather than having to sit at a regular table, taking up less room.