Despite the volumes of moans and articles on poor presentations, it seems like we are'nt getting any better at presenting, or creating slideshows.
I'm often asked how much text should there be on a slide, and the answer ideally is none.
The problem with slides is that the way presenters use them. The goal is to put something up that will briefly engage the audience, and then they should focus back on the presenter again. What sadly happens is that many presenters put essays up on their slides, and as the audience can read faster than they can listen, they will read the entire slide whilst ignoring what the presenter has to say.
So, back to text, ideally if you have to put text up on the slide, try an employ a 3 by 3 rule; 3 bullets, 3 words per bullet, and if you think this is too hard, start off with 6 by 6.
And lastly, font sizes; bigger is better. Size will largely depend on the equipment and environment you are presennting in, but keep fonts familiar (arial etc) with a minimum font size of 36.