I'm starting my third reading of Theodora Bynon's Historical Linguistics; the theory is that the more I read it, the more bits of it I will actually retain. Of course I've got a general idea of how things like sound change work, but I'd like to get a better understanding of the whole issue and Historical Linguistics is as good an overview as I've ever seen--if somewhat stuffy in flavor, having been written in 1977.
I think a large part of my problem is that IPA symbols just don't connect to sounds, especially vowel sounds, for me; when reading a book in which large chunks of the text are about this or that sound, this is obviously a problem. But I'm working on it.