I know I'm coming late to this but Lynne Truss's book "Eats Shoots and Leaves" is an absolute delight. I mentioned before that one reviewer made me feel giddy when I realised what a difference correct punctuation made to one passage but the feeling was short lived and has only been repeated as I read Ms Truss's book. Not only is it full of rules for the correct use of punctuation but it makes it clear what all the various marks are supposed to do.
One of the most striking sentences in the book is the description of punctuation as: "a courtesy designed to help readers to understand a story without stumbling." I had a real "man with the teeth opening the door" moment (Thanks, Ken) when I read that. Later in the book she talks about the feelings that good punctuation is supposed to provoke in the reader and I had another of those moments. I can now see how useful it can be in writing; how it can make improve what is said; how it can help. (Look at that - two semi-colons in a sentence. Astonishing.)
I suspect Ms Truss must be close in age to myself as she speaks of going through school and never having had any of the punctuation explained to her. Like me. She declares herself a stranger to subordinate clauses. Like me. But I guess that is grammar rather than punctuation but at least now I know the difference.
I suspect I'll have to re-read it to get the full benefit, and maybe copy out the rules, but I feel encouraged by how straight-forward she makes it seem. Doubtless it is not quite as clear-cut as she suggests but at least the basics are a bit clearer now.