Rails3.0.x to Rails3.1.0

application.html.erb

    <%= stylesheet_link_tag 'application' %>
    <%= javascript_include_tag 'application' %>

application.js

//= require jquery
//= require jquery_ujs

application.rb

#Bundler.require(:default, Rails.env) if defined?(Bundler) # <- delete this

# add
if defined?(Bundler)
  # If you precompile assets before deploying to production, use this line
  Bundler.require *Rails.groups(:assets => %w(development test))
  # If you want your assets lazily compiled in production, use this line
  # Bundler.require(:default, :assets, Rails.env)
end

module MyApp
  class Application < Rails::Application
    ...
    config.assets.enabled = true  # add
    config.assets.version = '1.0' # add
  end
end

development.rb

  #config.action_view.debug_rjs = true # <- delete this

Gemfile

gem 'rails', '3.1.0'

...

# add for assets
gem 'sass'
gem 'coffee-script'
gem 'uglifier'
gem 'jquery-rails'

gistfile1.txt

mkdir app/assets
mv public/javascripts app/assets
mv public/stylesheets app/assets
mv public/images app/assets
cd app/assets/javascripts && rm controls.js dragdrop.js effects.js rails.js prototype.js

production.rb

  config.assets.compress = true
  config.assets.compile  = true
  config.assets.digest   = true

routes.rb

-MyApp::Application.routes.draw do |map|
+MyApp::Application.routes.draw do