Nowadays, People tend to express their ideas with 100-page slides containing various transitional effects and fade-in/out elements to 'emphasis' their highlights. After experiencing that many 'slide exhibition' instead of presentation, I want to show some of my guidelines to those fresh slide-makers who presume their presentation could be better with gorgeous effects, hoping may thus slightly diminish these horrible situations.
General Guidelines: Alignment
One essential point of improving presentation slide design is that everyone should take much more efforts on alignment. Better alignment gains readability and clarity. Keynote Alignment Assistance is your good friend, few other softwares in the same category can compete Keynote on this feature. For more information on this subject, I highly recommend everyone to consult the book The Non-Designer's Design Book.
No (transitional) effects at all
Seldom people know how to make effects in their slides to function properly instead of disturbing the audience. Under these circumstances, I would perfer to work without these fancy effects. It can eliminate distractions of audiences.
Less information(text) on one slide
Presuming that all your audiences can not quickly understand while ones are talking about complex concepts, so they tend to slide to find some help. Having less text on one slide makes them perceive your idea very quickly and focus on speaking, Instead of making them trapped in quite an amount of texts striving for a clue.
Clearly indicate where we are / where we were
Again, presuming your audiences have pretty short-memory: When step-2 was shown, It would be better pointing out to them where step-1 was positioned as well. It provides not only user-friendliness but also clarity. Clearness is the king.