Sitting in on a presentation recently, I noticed that the speaker had a habit of advancing to the next slide well before he was ready to speak about it. He was almost finished with the previous topic and had not yet begun to verbally transition to his next point.
Instead of blacking out the screen until he began his next topic he was showing the upcoming visual before it made sense to the audience. I am sure everyone was preoccupied with figuring out where he was going. An unnecessary distraction.
The lesson: be aware of what you are saying and how it coordinates with what is on the screen. Show no slide before its time.