What is an effective presentation?

The speaker must use the slides as a blackboard and not as a textbook. i.e. He/She should use the slides to augment their talk and should not repeat what is written on it.

If they should not repeat what is written on the slides, then it should contain matter which can be understood by the audience without needing to shift their attention off the speaker's talk. i.e. very less Words, pictures.

Sometimes, lots of text matter on slides becomes unavoidable. Then, time should be given by the speaker for the audience to read thro' the slide before he/she talks about it. Otherwise the speaker will get only split attention which reduces the effectiveness of the speech.

As well, it is most important to give an outline at the start and a summary at the end. Most listeners are comfortable when they know what will come next. Their preparedness will help the speaker to move to the next topic easily.