Here is the most modern approach to gem crafting with Bundler:
bundle gem your_gem cd your_gem
edit your_gem.gemspec and add description, summary and optional website. Add required gems such as rspec to the Gemfile.
rspec --init touch spec/your_gem_spec.rb
Write good tests. Add your code to lib/your_gem.rb. When you're finished its time to build and push to rubygems.org:
gem build your_gem.gemspec gem push your_gem-0.0.1.gem
And thats it. Next time you make a change be sure to change the version number in version.rb.