The hierarchy of slides goes something like:

    Relevant images which support the speaker
    Relevant graphs, rendered for projection
    Relevant microcopy which gives context or focus
    Relevant videos which are kept as short as possible
    Bullet slides which double as effective microcopy

    Bullet slides which double as speaker's notes
    Most slides which animate in point-by-point
    Irrelevant or unnecessarily long videos
    Unreadable diagrams
    Unreadable walls of text

The zeroth rule of presentations is don't waste your audience's time.

Michael Alley describes an "Assertion-Evidence" structure for slides, in which the heading becomes something more like a sentence that states the point, and the rest of the slide presents evidence in support of that. http://www.writing.engr.psu.edu/slides.html

This approach tends to do away with traditional headings altogether, so it tends to push you in the same direction as, or even a step beyond, the production-oriented advice given here.

You shouldn't even have text at all on the bottom half of the slide. Text on a slideshow presentation should be minimal. The audience should be listening to you, not reading your slides.

That seems like rather venue-specific advice. In the average lecture hall or conference room I've presented in, all the seats can see the full screen just fine.

In fact, I've sometimes put important graphics as low as possible, knowing the lights in a particular room tended to wash out the top half of slides a bit.

Also, don't save the best for last. In the first slide put the results/outcome/point of your presentation and THEN explain how you made such a brilliant deduction in the rest of the deck. Its not a movie, you're not there to create drama and keep us on the edge of our seats pining for the answer, you're there to transfer information - optimize for this.

Now that I'm a crotchety old man, my zeroth rule of presentations is to always use the bathroom before presenting.

Actually, it's a good idea for anyone. Get everything in order, because you're talking for up to an hour. You don't want to be in the middle of a talk and some part of your brain pokes you about not having used the washroom, and another part of your brain idly speculates about how the audience would respond to an intermission...

Same with eating a reasonable while beforehand. Not too close to the talk, so you're not processing food too much while talking, not too far before... Helps your distributed mind care about your audience. And sleep helps you improvise better and have a sharper sense of humor.

Surely it's "know where you're presenting".

This is what I hate about these "I put up funny photos and slap some clever sentence below them"-style presentations. If you're not sitting in the front row, you cannot read anything.

This is a handy tip but calling it the zeroth law just because a cranky blogger got stuck at the back of a presentation is extreme.

I'd say it was "know what you're talking about".