Step 1: Identify constraints
1) How many people will attend?
This is the big one. If you've got more attendees than tables, chairs, plates, silverware, etc then you'll have to devise work-arounds. Tables/chairs can be rented, borrowed from friends and neighbors, or improvised from milk crates and pieces of plywood or spare doors. If you're short plates and silverware you can decide to use disposable or ask guests to bring their own, picnic style. Make your own cloth napkins to be extra-cool.
2) Who's making/bringing food?
Identify what you'd like to make, and what (if anything) you'd like your guests to bring. Make sure your guests are on the same page with this.
3) Buffet or table service?
If you've got more than one table a buffet is pretty much required. It also reduces the need for small, passable bowls which would otherwise require refills. You can put the whole dish on the buffet and be done with it.
4) Storage space
How much space do you have in your refrigerator and freezer? This determines what you can make ahead. If you live in a cold area an enclosed porch or deck can supplement your fridge/freezer space; if it's too warm out you can use an ice-filled cooler to bulk up your refrigerated space.
How many ovens/racks do you have? You'll need to block out time accordingly, and choose oven vs. stovetop preparations as necessary.
What time do you plan to serve dinner? This one is under your control; pick a time that will allow you to wake up at a normal time and still be able to run everything through the oven with time to spare. Schedule this one for your convenience.