Updated: September 12, 2013
A couple of people have been asking my where to start with Rails. I usually say it's easy! Just learn ruby then learn rails.
Well it's time to put my money where my mouth is. Here is a guide with some helpful resources on how to learn rails.
Step 0: Tools & Setup
I love Sublime Text so much. It's pretty much an IDE once you customize it with plugins. If you really need an IDE you can try something like RubyMine. I've only used it a little and can't really speak it its usefulness.
Neither of these tools are free but you can use Sublime Text indefinitely if you're okay with a pop-up every now and again.
If you're on a Mac then you already have ruby 1.8.x, so you can use that before installing anything. If you're on any other platform visit ruby's webpage. As of today, the two choices of ruby that you'll have will probably be 1.9.3 and 2.0.0. Go with 2.0.0.
I highly recommend that you use rvm or rbenv once you know what you're doing but, installing either one of these can be daunting task so it's okay to skip this step while you're testing the waters. Do not forget to do this at some point; I personally prefer rbenv.
Step 1: Ruby
You'll hear a lot of people say that you don't need to learn ruby to be able to work in Rails. This is false. Well, as a programmer I think it's better to learn the language and it's quirks before diving into a framework.
Try ruby is a great place to start. The tutorial doesn't take long and is definitely worth doing.
Once you've tried ruby, head on over to Ruby monk and see if you actually picked up on anything.
Project Euler (Bonus)
If you want to truly tap into your ruby powers, a good place to do that is Project Euler. Register for an account and do a bunch of the problems using ruby.
Step 2: Rails
This is a quick 'course' by the same people that made Try Ruby. It's a bit tricky, and you might be confused at some points, but it'll definitely give you an idea of what Rails is about. Do it.
This is a great book and this is how I first go into rails. Also, the entire book is available for free!
Once you've read the book, you're good to go! You can now do Rails.