This is a broad question that covers a number of different aspects, so I won't go into detail here. However, these are some general areas that will hopefully help with initial research and reading for you.
In terms of Information Architecture, conveying information to a user efficiently involves the effective use of chunking to group information into logical sections, and then creating a consistent flow through the different sections depending on audience or intent.
In terms of visual design, conveying information to a user efficiently involves creating clear visual hierarchy by spacing, density of content (words per line, paragraphs per page) as well as more complex design assets like charts, graphs and infographics.
I think that will probably be enough for you to start delving into things further, and if you have more specific questions please post another question.