I recently relearned RoR after not using it for a while. I was recommended http://pragprog.com/titles/rails2/agile-web-development-with... and I definitely found it to be a good book.

What helped me the most was to just jump into a project and start coding. I decided to try to do a clone of twitter, just to see if I could get that working. It helped that I had a few friends who were good rails hackers that I could go to with questions.