The content of this book offers a great introduction to gulp, but there are many additional resources that are resourceful, as you continue to use and learn more about gulp. As you move forward, I highly suggest that you take a look at these resources to pick up on additional tips and examples that were outside the scope of this book.
If you're interested in a more thorough explanation of streams and how they work, then substack's stream-handbook is exactly what you're looking for. This is one of the best available resources for streams on the Internet. For more information, refer to https://github.com/substack/stream-handbook.
NodeSchool is a fantastic command-line resource for learning many different types of languages and technologies. This is a great place to learn more about both node.js and streams; you can then put your newly acquired command-line skills into practice.
If you would like to learn more about node.js, be sure to check out the learnyounode course. If you're interested in learning more about streams, the stream-adventure course is just what you're looking for. For more information, refer to http://nodeschool.io/.
The gulp community keeps an updated list of "recipes" for common use cases in the official gulp documentation. These recipes are great to implement into projects or use as starting points for more advanced uses. For more information, refer to https://github.com/gulpjs/gulp/tree/master/docs/recipes.