What resources can teach me to draw floor plans by hand?
Drafting "by hand" is still taught in most architecture (and often civil engineering) schools. AutoCAD is simply one tool in the toolbox of a draftsman.

So, I would look for a book on basic architectural drafting. You might see if you can get in touch with the drafting teacher at your local high school or community college and see what he uses as a textbook.

As for being able to "sketch" ideas, only the very roughest plans are drawn freehand. Artist's renderings and some elevation drawings will have an element of freehand to them, but the main lines of the building will be drawn with the paper taped to the drafting table and using a straightedge and speed squares.