1. What's my total budget? And what are my priorities with that budget?
2. How many people am I expecting?
3. How formal/casual do I want the event to be?
With smaller, intimate events, I generally go with real plates. Once I start inviting 12 or more, I generally go with paper plates. (I'm not talking weddings here - those are their own animal - I'm talking about any other kind of party.) Either way, plates can function as accessories to your theme, or even as the whole inspiration for the theme.
Ever wondered how many forks you're really supposed to have? And what do you use them all for, anyway? Well, it depends on the kind of event you're hosting. Sarah at Toast and Tables wrote a wonderful post on the proper way to set a table - for everything from a casual lunch to a formal dinner party. She even included "maps" that show you exactly where you should place each item...read her post here for a quick education.
More resources: check out Martha's Party Planning Guide
Image 1: Crate and Barrel Orchid Dinnerware
Images 2 & 3: my (tiny) inspiration boards from www.platesandnapkins.com
Image 3: Toast and Tables blog
Image 4: Martha Stewart Living