I certainly didn't coin the phrase “Less is more” but I'll apply it to mobile multimedia content because it captures the essence of what should be guiding your content development when building for mobile distribution. On a mobile device your viewer will have less real estate for the visual aspects to appear. This makes your use of text critical, and your reduction of the use of text even more critical.
The key is that your visuals supports the narration and not the other way around. The power in the presentation comes from the audio delivery and messaging, not the visuals. Think about having a story read to you as a child. You sit and listen to the story and then periodically you get to see an image that supports your vision of the message. This should be the experience of your viewer. Not only will they appreciate that they did not have to use brain power to decipher 10 pt. font on a smartphone, the will recognize the method and appreciate the ease with which they can absorb the content. Speaking of brain power, it takes both sides of the brain to process images and audio and the key to getting the message across is to not overwhelm the visual part of the cortex while the audio is being processed.
Here are some specific recommendations:
Design for the small screen
Use 32 pt. font or greater to insure easily read words
Use the Rule of 5
No slide has more than 5 bullets
No bullet has more than 5 words
No word has more than 5 letters (whenever possible)
Whenever you can use a single image and no text at all
A picture is worth a thousand words
Use contrasting colors so that text is easily viewed
Don’t fill the slide – allow clean empty space to flourish.