Dim the Lights
If you don't have dimmers then switch out your regular bulbs for a lower wattage bulb (or a pink bulb) just for your soiree. It might seem dark at first but you'll get used to it and your guests will feel cozier.
Light from 3 Sources
Ever been in a restaurant and felt like you had a spotlight on your face? You knew it was actually happening because you looked around the table and everyone had ghastly shadows contorting their faces? Avoid this in your home by having at least 3 sources of light in each room and avoiding harsh overhead light. Remember Ron from the Smallest Coolest Contest a coupe of years ago? He had 11 lamps in a 300 square foot studio. And it looked KILLER. Now you probably don't need that many, but start with 3 and see how it goes.
Add a Tablelamp to the Bathroom
Often the Bathroom gets overlooked, so make sure the light is flattering and keeps the ambience you've created in the rest of the house. You can either try to try a tablelamp or add enough candles (and far away from the towels) so that your guests don't need to reach for the overhead light switch.
What tricks do you have for party lighting?