Buy one. Seriously.

Install it so it turns on and begins recording whenever you start the car.

It needs to have as much view of the road as possible with just the front of your vehicle in the frame — nobody cares about video of the sky; there aren’t any cars up there.

Check it periodically to see that it’s working.

Remember: out of sight, out of mind.

And, a couple of things you’ll need to do to cover your own ass, legally:

1. Turn off the ability to record audio. Seriously. If you’re using it to capture the actions of others, then disable the ability to also capture your own comments — remarks you make will always be self-incriminating. And in several places, audio recording falls under evesdropping or wiretapping laws.
2. Don’t ever get into a verbal altercation with somebody else and “threaten” them with facts that they simply don’t need to know. For example, pointing to the dash cam and exclaiming, “This is on camera!” Don’t advertise that it even exists.
3. If you intend sharing anything “as evidence”, you’ll need to ensure you save that particular clip, in its entirety, unchanged and unedited, until the statute of limitations for the alleged offense expires. How long is that? Well, it depends on the alleged crime. But for the rest of your life is a real possibility.
4. If you at any time feel the need to delete potentially self-incriminating videos… don’t. Seriously. Look up “spoliation of evidence”. In several locales, it falls under “destruction of evidence”.
5. A dash cam is as much a silent witness of somebody else’s actions as it is a witness of your own actions. It’ll see other people driving dangerously just as easily as it’ll see you doing the same. I suppose the takeaway would be: don’t drive like an imbecile.

Oh, and I’m not a lawyer — but ignorance of the law is no excuse.

This has been a public service announcement.