The more free space in the fridge, the better. Make the big trip to the grocery store a week ahead as well. Most items, with the exception of salad greens and some fruit, will keep for a week. If you're baking cookies for the party, prepare the cookie dough in advance and freeze it. If you're serving a decorated cake, make and bake the cake parts a week or more ahead of time, wrap them well in plastic wrap and freeze them until the day before.
Frozen cakes are easier to decorate than thawed ones anyway.
Set the table and ready your home two days ahead, if seating people at a table for dinner. This will give you enough time to buy or borrow things you may need. Consider serving the meal as a buffet if you want to serve more guests than your table will seat. Set the table against a wall near the kitchen and use it as the serving area. For buffet service, make sure to divide all the food into small portions.