Use a sharp bread knife to cut the baguette across the center of its horizontal axis. For an even cut across, place your left hand flat and firmly down on the top of the baguette, and begin sawing the middle of the baguette with the knife in your right hand.
Here's another helpful tip for getting an even cut: bend down so the knife is at your eye level, and always make sure the knife is parallel with the cutting board as you cut.