Here's Tomm from RocketJump Film School to show you the basics of how to do it right, plus some very tangible examples of how not to slate.
There are a few things that I would add to the practices in the video. First, if the information is available, always include the clip name/number from your audio recording device on the slate. This little step can make the editor's life so much easier when it comes to matching video clips with the proper external audio. Secondly, it's important to make sure the slate stays roughly the same size in the frame regardless of shot type or focal length. If you're shooting a wide shot on, say, an 18mm lens, but you slate near the actor's face (with soft sticks hopefully), chances are that the editor or assistant editor is going to have a very difficult time reading the information on the slate. Conversely, if you're shooting an extreme closeup on a 135mm, but you hold the slate 5 feet away from the lens, chances are that the slate will take up the entire frame and only some of the information will be visible. Hopefully the camera operator would prevent both of those instances from happening, but it doesn't always happen that way.
The trick that I've always used for keeping the slate the same size in the frame regardless of focal length is really simple, and it works like a charm. Essentially, for every 10mm in focal length, you hold the slate one additional foot from the lens. Here are a few examples:
For an 24mm lens, holding the slate roughly 2.5 feet away will make it the perfect distance for the editor to see all of the information and the clap. For a 50mm, you'd hold it roughly 5 feet away. For an 85mm, roughly 8.5 feet away. For 135mm, closer to 13 feet way. And so on.
This little formula may change depending on the sensor size you're working with, but for super35, it works like a charm. I'd imagine that if you're shooting with a M4/3 or super16 sized sensor, you'd want to effectively double it -- so it becomes 2 feet for every 10mm, give or take.
Do you guys have any slating tips or best practices that we're shared here? Let us know down in the comments!
Source: Rocket Jump Film School