These books kick-started my journey to understanding (and appreciating) the use of diagrams, colors, fonts, and imagery for the purpose of conveying an idea.
I'd suggest also watching Larry Lessig. He puts almost no information on any individual slide, but he gets his meaning across with about 4 slides per minute. He often repeats slides for emphasis.
In a tech talk, you'll never quite match his style. But getting halfway there can improve many talks.
There are two books which have made me better at this:
1. The back of the napkin [http://www.thebackofthenapkin.com/]
2. Slide:ology [http://blog.duarte.com/book/]
These books kick-started my journey to understanding (and appreciating) the use of diagrams, colors, fonts, and imagery for the purpose of conveying an idea.
Update: Added links.