If your video card and AE play nice together (you'll be able to tell if they don't if this tip doesn't work), you can use AE 6.0's new OpenGL renderer to display animating 3D layers faster.
Click the OpenGL button at the bottom of the Comp Window. Select OpenGL with Static Textures if you're animating still images that are moving around in 3D space. Select OpenGL with Moving Textures if you're animating videos moving around in 3D space. Actually, you may want to choose the Static option even if you're animating videos , because the display will speed up even more, but video layers will freeze on their first frame.
OpenGL speeds up display only while you're working in the Timeline. It does not speed up the final render. And you can't use it to RAM preview your animation. Still, it really speeds things up when you're dragging 3D layers around in the Comp Window, scrubbing the Current Time Indicator or hitting the spacebar to play.
Most AE Effects won't display while OpenGL is active. The effects will still render, but you won't see them while you're viewing your Comp using OpenGL.
To check which video cards play nice with After Effects, see http://www.adobe.com/products/aftereffects/opengl.html.