1d12 + 1d8 table is commonly used for
random encounters, because it gives a nonuniform distribution where
some outcomes are more likely than others. But why stick to that?
By rolling one of the dice with advantage or disadvantage, you get
a very different distribution, and can make one table work in many
A lot of GMs advise rolling behind a screen, so you can fudge rolls when you get a result which would be bad for the story. I think that at best fudging is unnecessary, and can be remedied by being more thoughtful about what rolls you ask for (and I go in to how I think about rolls), and at worst cheating, where you’re explicitly ignoring the rules of the game.