When rendering from After Effects make sure your specifying the right compression. The default is usually animation which is always pretty big as it’s pretty much uncompressed video. Before hitting ‘Render’ click on the orange text to the right of where it says ‘Output Module’.
Here you can specify your format and compression. Quicktime movie is normally the best format. To specify your compression, click on ‘Format Options…’ and you’ll see a range of different compressions you can use. The one you choose all depends on what your using your final video for. If you let me know I’d be happy to help you with some settings.
KJ