http://www.w3schools.com/js/ has a very clean, straightforward tutorial with complete reference. My advice would be that as you learn you should take notes in form of questions, so instead of writing: "To declare a function: function name (...) {...}" write a question: "How to define a function?" Then rewise your questions after each chapter and write your answers on a piece of paper, not into the computer - you'll memorise the syntax faster and better.
After reading the entire tutorial you should have about 8-10 pages of notes with questions. If you don't remember how to write something, go back to the online tutorial/reference and find what you need.
At the beginning don't spend too much time on the Math or Date functions, as these won't be that much useful. Focus on Strings and Arrays instead, regular expressions are also fun to play with.
And after you're done with the basics you could try the Design Patterns: http://addyosmani.com/resources/essentialjsdesignpatterns/bo...
Thirdly: as you learn you should try to build things that could be useful for yourself and that you would enjoy building. For instance you could try to make a simple flashcard system or a little script that could strip a given string from HTML tags, or a script that would create numerated footnotes on your website. Something like 150-200 lines of code.
Your could also play with manipulting SVG elements with your JS - it's very rewarding and I believe that as for a beginner it's important to SEE the effects instantly.