Here are a few pointers:
Time based effects such as ‘echo’ increase render time dramatically.
Some video codecs use interframe compression in which the current frame may not be a full frame (I Frame) but actually an intermediary frame (P or B Frame) that holds information about what has changed since the last full frame. Basically what this means is that, although the file size of the compressed video is smaller, AE has to take lots more time to render the intermediary frames. The major family of codecs that use this scheme are MPEG and its derivatives MPEG-2, H.264, AVC, HDV, etc. Instead of using MPEG footage in your AE project, consider transcoding to a high-quality, intraframe compressed codec such as Photo JPEG at Max quality.
If there are animations/effects going on in your pre-comps then these will obviously add to render time. You should consider pre-rendering your pre-comps (Composition>Pre-Render) once they are finalized. Note that this will not work properly if the pre-comp has its “Collapse Transformations” switch on in the final comp.
Shadows increase render time significantly, do you need lights? Is there a way to fake it that will look just as good? You can also consider decreasing the Shadow Map size in Composition Settings>Advanced>Options>Shadow Map Resolution.
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA