Begin each slide with a headline sentence, not just a topic phrase.
Examples:
Drosophila [bad; too vague]
Drosophila Hmx gene [bad; so what?]
Drosophila Hmx gene directs mouse
inner-ear development. [good; asserts an interesting claim]
Use large fonts and simple layout for easy reading.
Rules of thumb:
Use no more than 8 words/line, 8 lines/slide maximum.
Can you read it easily if you stand over it on the floor?
Choose images carefully not to decorate but to reveal
Consider progressive disclosure when sequence is important
(sticky notes can help here).