Hey,
I can't recommend you the best way, but I can tell you how learned and started to love Node.js
Coming from Java over Ruby to Node.js. Thanks to Ruby and Sinatra, I learned how easy it can be to write REST services with a super simple grammar.
In Node.js, some guys started to extend the HTTP module of Node.js. They tried to mimic the API of Sinatra and called it Express.js.
Head over to http://expressjs.com/ website and hover with your mouse above the Getting Started section and select 'Installing' and then 'Hello World'. Then the Basic Routing example, which is the concept key in my opinion. If you did that, you can write simple backend services.
For more advanced topics, see the Guides section.
Why should you learn Express.js when you are asking about learning Node.js? Well, Express.js sits on top of Node.js. It doesn't hide stuff away from you.
If you think you are ready for more, then npmjs.org should be your next goal. Have fun!