Example refactoring of https://github.com/halostatue/mime-types/blob/d4f761ded1/lib/mime/type.rb#L155 for a reply to https://news.ycombinator.com/item?id=7339958.

0-mime-type.rb

class MIME::Type
  # Compares the MIME::Type based on how reliable it is before doing a
  # normal <=> comparison. Used by MIME::Types#[] to sort types.
  def priority_compare(other)
    PriorityComparison.new(self, other).value
  end
end

1-mime-type-priority_comparison.rb

class MIME::Type::PriorityComparison
  def initialize(one, two)
    @one, @two = one, two
  end

  def value
    if simplified_value.zero?
      complex_value
    else
      simplified_value
    end
  end

  private

  def simplified_value
    one.simplified <=> two.simplified
  end

  def complex_value
    if one.registered? != two.registered?
      one.registered? ? -1 : 1 # registered < unregistered
    elsif one.platform? != two.platform?
      one.platform? ? 1 : -1 # generic < platform
    elsif one.complete? != two.complete?
      one.complete? ? -1 : 1 # complete < incomplete
    elsif one.obsolete? != two.obsolete?
      one.obsolete? ? 1 : -1 # current < obsolete
    elsif one.obsolete? && (one.use_instead != two.use_instead)
      use_instead_value
    else
      0
    end

    def use_instead_value
      if one.use_instead.nil?
        1
      elsif two.use_instead.nil?
        -1
      else
        one.use_instead <=> two.use_instead
      end
    end
  end

  def attr_reader :one, :two
end

Intended as a kind of minimal extraction/refactoring – extracting the object and breaking up the nested conditionals. More could be done, of course, but with diminishing returns.