If you're planning on shooting with multiple cameras and audio recorders, you could potentially wind up spending a hell of a lot of time syncing it all in post. Thankfully, Film Riot's here to show you a bunch of quicker ways to do it.
There's a little bit of everything for everyone in this video, which I like. Host Ryan Connolly doesn't just say, "Hey everybody! Go buy PluralEyes and you'll be golden!" I mean sure, if you've got the cash, do it. It's worth it. But, not everyone has $200 to spend on audio synchronizing software.
Luckily, there are a bunch of great tricks of the trade to learn here, like synching audio by matching up waveform patterns. One thing to remember, though, is that you should always record audio in-camera (if possible) so you have a scratch track to work with and reference -- or to, heaven forbid, use in the event of the worst kind of filmmaking misfortune. Though this might not be ideal if you've got a ton of audio tracks, it's simple and easy and doesn't require expensive software.
Another thing to know about is how to utilize a slate -- or clapperboard, sticks, sync board, marker. Whatever you call it, it's used to give both audio and visual queues for synchronization later. Of course, physical slates and slate apps not only make you look super cool and profesh, but they let you input a bunch of pertinent information on them for use in post later. However, they do tend to be pretty spendy. The iOS app MovieSlate (which was used in the video above) is definitely a great one -- I've used it a bunch of times -- but it's $30. And the physical slates are at least that much. But the purpose of a slate isn't necessarily just for knowing the scene numbers and which take it is. Again, it's for synching. So, if you're without one during a shoot, a good, ol' fashioned hand clap (you can get fancy and do a mid-air high five, as well) will do the trick.