for using icons easily, i add helper methods in application_helper.rb. I made this for icomoon, but i think you may be able to use this with Font-Awesome, Twitter Bootstrap2.0 (not WebFont but png icons) and Bootstrap3.0.

application_helper.rb

  # to make <i> easily.
  # name: icon class name.
  # data: webfont number.some webfonts like icomoon can use with this.
  # color: for Bootstrap2.0. you can set this 'white' for white icon.  
  # class: you can set css class to <i> tag.
  # style: you can set inline css to <i> tag.
  def icon_tag(options)
    raise unless options.present?
    case options
      when String
        name = options
        data = ''
        icon_color = ''
        icon_class = ''
        style = ''
      when Hash
        name = options[:name].presence || ''
        data = options[:data].presence || ''
        icon_class = options[:class].presence || ''
        icon_color = options[:color].present? ? ' icon-' + options[:color] + ' ' : ' '
        style = options[:style].presence || ''
    end

    raise if name.blank? && data.blank?

    if name.present?
      if style.present?
        content_tag(:i, '', :class => "icon-#{name}#{icon_color}#{icon_class}", :style => "#{style}").html_safe
      else
        content_tag(:i, '', :class => "icon-#{name}#{icon_color}#{icon_class}").html_safe
      end
    else
      if style.present?
        %Q|<i data-icon="#{data}" aria-hidden="true" class="#{icon_class}" style="#{style}"></i>|.html_safe
      else
        %Q|<i data-icon="#{data}" aria-hidden="true" class="#{icon_class}"></i>|.html_safe
      end
    end
  end


  # to use icons, extend link_to from url_helper.rb
  # you can use this like below.
  # <%= icon_link_to 'edit', '#', :class => 'btn launch_modal', :target_id => '#info_modal', :icon => 'pencil-2' %>
  # <%= icon_link_to 'download files', path.to.url, :target => '_blank', :class => 'btn', :icon => {:name => 'download-3', :align => 'left'}  %>
  # <%= icon_link_to 'pupup', '#', :icon => {:name => 'checkmark-circle', :class=>'text-success'}, :class => 'btn primary launch_modal', :target_id => "#edit_modal" %>
  # arguments are same as link_to except ':icon'.
  # with this, you can easily buttom formed link with icons, like github.
  def icon_link_to(*args, &block)
    if block_given?
      options      = args.first || {}
      html_options = args.second
      icon_link_to(capture(&block), options, html_options)
    else
      name         = args[0]
      options      = args[1] || {}
      html_options = args[2] || {}

      icon = html_options.delete(:icon)
      raise unless icon.present?

      case icon
        when String
          icon_align = 'left'
        when Hash
          icon_align = icon[:align].presence || 'left'
        else
          raise icon.inspect
      end

      if icon_align == 'left'
        link_to(options, html_options) do
          (icon_tag(icon) + " #{name}").html_safe
        end
      else
        link_to(options, html_options) do
          ("#{name} " + icon_tag(icon)).html_safe
        end
      end
    end
  end

  # to use icons, extend link_to from form_tag_helper.rb
  # if you use submit_tag, perhaps you can replace only method name to this and add 'icon' property.
  # you can use this like below.
  # <%= icon_button_tag 'make finished', :class => 'btn primary mrgn_r', :icon => 'stop', :confirm => 'are you sure finishing this job ?' %>
  # see icon_link_to also.  
  def icon_button_tag(content_or_options = nil, options = nil, &block)
    options = content_or_options if block_given? && content_or_options.is_a?(Hash)
    options ||= {}

    if block_given?
      content = capture(&block)
    else
      content = content_or_options
    end

    icon = options.delete(:icon)
    raise unless icon.present?

    case icon
      when String
        icon_align = 'left'
      when Hash
        icon_align = icon[:align].presence || 'left'
      else
        raise icon.inspect
    end

    if icon_align == 'left'
      button_tag(content_or_options, options) do
        (icon_tag(icon) + " #{content}").html_safe
      end
    else
      button_tag(content_or_options, options) do
        ("#{content} " + icon_tag(icon)).html_safe
      end
    end
  end