Best practice of extracting dependencies of gems

If we keep introducing gems to another gem, it often leads to a mess. In such a case, we can extract dependencies to a gem that bridges two gems. I've looked into pry-rails and rspec-rails but still cannot find things common between them. Is there a best practice to create such a bridge gem(in terms of a way to define gemspec, to extract Rails dependant code, to define monkey patch etc)? thanks