Prep and lesson plans is half the battle. The other half is subject knowledge, which gives confidence.
I avoid Powerpoint as much as possible, and if I do use it, its generally as a very visual aid only. I did a lecture for army cadets on camouflage and concealment, which was all colour pictures. No text, but lots of discussion and questions to and from the class. Fancy powerpoint graphics and dissolves just make you look like you know a lot about .ppt but little else.
Research, apparently has found that if you use text, people learn from text. If you use images, people learn from images. If you mix the two, it causes confusion and parts of the message are lost, because the same area of the brain processes text and images, but not at the same time or in the same way.
In ref to Powerpoint Presentations (US) 'In a hail of bullets'
"It's dangerous because it can create the illusion of understanding and the illusion of control, he said: Some problems in the world are not bullet-isable, other commanders say Powerpoint discourages decision-making and discussion and keeps junior officers, called Powerpoint Rangers, occupied preparing slides.