Here is great video – another one from WinkSound – about organizing all your tracks in preparation for mixdown. Remember, mixing down your tracks is one of three major steps/jobs in a recording project. Recording/tracking is the first step, then comes mixing, and finally there is mastering. See our post here: Recording Engineer, Mix Engineer and Mastering Engineer – Oh My for a reminder of that.
Anyway, when you have a lot of tracks to mix down, usually in a music project (not so much with a voice-over project usually), you need to organize things a bit before you dive into the mixing job. In this video, Michael White shows you how to do just that. This works for any multi-track recording software, Reaper included.