If you have something for students to read on a slide (even just one bullet point) wait in silence while they read it. If there is something to copy down give them time to do that before talking about it.

This is actually more difficult than it sounds! And you have to judge it so that you don’t wait too long either – I usually wait until at least half of them have put their pens down and are looking up at you.

They can’t fully take in what you are saying, and certainly can’t think it through if they are copying something else (even if related) at the the same time.