Been working with Ruby On Rails on & off for about a fortnight. A few observations for those starting to pick up this framework,
1. Keep Dave Thomas' excellent text by your side at all times
Dave Thomas, co-author of the 'Pragmatic Programmer' series, is a worthy guide to Ruby. This text is excellent - Programming Ruby: The Pragmatic Programmer's Guide. Also keep Matz's original Ruby manual to hand. It's fun.
2. Use Rake
Rake is a ruby makefile-style utility. It's useful. Try rake --tasks to check the available tasks. You can define your own rake tasks in the Rakefile sitting in your application's root directory. You can define dependencies between tasks and files. It's useful for deployment, sql dumps, code stats, documentation generation etc. In addition to the built-in tasks, you can find :deploy and :rollback tasks out there if you root around, allowing you to version your application formally.
3. Use Gem
Gem is the CPAN for Ruby - it fetches 'gems' - ruby modules/extensions. You'll need to use it to get your database adapter and other utilities.
4. Use Rdoc
Rdoc creates documentation from Ruby classes and spits it out in HTML format. I have a bookmark group in my web browser made up of Ruby and Rails standard libraries. Cmd-click in Safari makes all the tabs load in one go. I'm sure Firefox has an equivalent.
Note: All three of these command line utilities (rake/gem/rdoc) are for Ruby in general, and exist independently from Rails. However, they will come with your Rails install.
5. Use the logs
Use the logs in the ./log directory. I always keep a unix screen open with
tail -f ./log/development.logrunning in it. This is the best way to get a feel for how ActiveRecord behaves in terms of database calls. To write to the log, use
logger.info("message here")6. Use Rexml for XML parsing
Most projects have some XML parsing going on - REXML is the most complete XML parser for ruby. You'll need to install it - it's not stdlib. Google it.
7. Take the time
RoR is encouraging a whole load of web developers to enter application development. This can be a good thing. However, it's a different ball game, so to speak. For starters, understanding the Model View Controller (MVC) design pattern is crucial to RoR. It's pretty simple, but you need to be able to apply it smartly in order to keep things neat as your application progresses. Understanding the role of testing and code versioning is also really important. Take the time to learn common application development and design techniques/patterns if you're coming from a web background. Your test code should usually outnumber your production code.
8. Get the Ruby syntax highlighting module for BBEDIT
When developing locally i like to use the BBEDIT text editor, because the cli editors start hurting my eyes. You can set up a project using New > File Group. The ruby syntax highlighter is here.
9. Check the irc channel
#rubyonrails at irc.freenode.net - nice people on the whole.
10. Using Webrick/Apache
First off, use the Webrick server while testing. More here. That's another unix screen i have running continually. If you want to test under Apache, turning on fast-cgi is explained here.
Finally
Feel confident. Rails is an enterprise level framework taking it's first steps - don't let the J2EE crew drown you out. Ruby > Java in spirit and in tone, even if Ruby's gem pool still has a long way to go to match the colossal Java API or Perl's extensive CPAN libraries. In terms of RoR: The framework is there. It will grow by virtue of the agility it encourages.
I'm still yet to find any particularly great apps in Rails since the 37Signals ones, but here's a simple code snippets library produced in RoR - Snippets. Keep an eye on the OS X and Ruby sections as they grow. I like the simplicity of this tool.