Say the DC

Probably one of the smallest changes with the biggest impacts you can make to your D&D game is to start saying the DC or AC explicitly before the dice hit the table.

Instead of:

— Make a strength check.
— I rolled a sixteen.
— OK, you made it. This-and-this happens…

Try:

— Make a DC 15 strength check.
— I made it.
— OK. This-and-this happens…

Or even, depending on circumstances, be very explicit about stake:

— This-and-this will happen if you can make a DC 15 strength check.
— I made it.

Why?

Clear outcomes, tension. Making the game feel more tangible. Especially if you aren’t fudging, this style helps convey to the players on every level what’s at stake here.

Otherwise, it’s so easy as DMs to slip into a pattern of not even having a DC in mind, just judging the die roll. That can lead to you sometimes being loosy-goosy. It can also lead to the character’s stat being kinda meaningless and the game just devolving into “die judging” A natural four is a banana peel slip and a natural eighteen is godlike grace and anything in between is “the story gets pushed in the direction the DM wanted it to get pushed”.

But sometimes the character doesn’t know how difficult something is?

Say the AC or DC after they’ve committed to the action, but before the dice hit the table.

But doesn’t this mean there is more time-wastey things said at the table?

No. Check out the two examples. If you don’t say the DC, the player will have to say the number. If you do say the DC, the player won’t have to say the number. It’s the same.