Personally I think that it's better to start off by understanding JavaScript. I recommend JavaScript: The Good Parts by Douglas Crockford to anyone who is starting out, particularly those who are experienced with other languages. The syntax of JS makes the language seem deceptively familiar. Once you are comfortable with JS then you will probably know how to best approach learning jQuery (if you can just read docs/examples or if you need to read a more instructional book like those which have been suggested). I never "learnt" jQuery. To me it's just like any other library and I read the docs for usage, but I actually prefer not to use it when I don't need it.
