Learning to read plans is much like learning to read books. After you've seen a few, you understand that every author has a different style and way of telling a story.
Architects do the same with drawings, which are really just "stories" about how to build. The more you read plans the better you are at understanding the ideas behind them.
Then it becomes easier to combine your own ideas with ideas you have seen in others.
I just added this book to the book review section (http://www.countryplans.com/books.html). Go there for the full review or click the link below to see it at Amazon.
(http://images.amazon.com/images/P/0486421562.01._PE32_SCMZZZZZZZ_.jpg)
http://www.amazon.com/exec/obidos/ASIN/0486421562/countryplans.com
Interesting. When I took classes in college on this subject we used a book titled "Basics for Builders: Plan Reading & Material Takeoff" by Wayne J. DelPico. I found the book very comprehensive and that class has proven to be one of my most valuable classes as a Civil Engineer (it sits on my reference shelf at work still). The book and course not only explains how to read plans but how to do material takeoffs and cost estimates. There are also some simple framing details in the book. The final project for that class, using nothing but the book for lectures, was to do an actual takeoff and estimate on a real set of house plans.