I would prefer people would go vegan, but this is a great first step. Go Meatless on Mondays:

If we all just commit to one day a week without eating meat, the effect will be great over the course of the year:

• Our greenhouse gas emission reductions equal US switching from a car with average fuel efficiency (that’s about 22 mpg for the entire fleet) to a high efficiency car such as the Toyota Prius (50 mpg).
• We will save about 1 ton of water, enough to fill up the bathtub 22 times per week
• If everyone in the US did this, we’d collectively save about 12 billion gallons of gasoline

(from TreeHugger)

While you are checking out the Meatless Monday website, make sure to check their recipes, such as Zesty Carribean Banana Muffins.