Today, looking something else up, I came across the Wikipedia entry for the Lesser Banishing Ritual of the Pentagram. It's not a bad summary and I thought I'd link it here for those who'd find it helpful to have an overview of the ritual in their files.
The occult world has gotten saturated with this ritual tech and understandably a lot of people are fed up with it. People also rightly point out that it is not the most comprehensive banishing nor the most venerable that can be performed.
Still, I love it; it does good (predictable, scalable) things for me; and it remains part of my daily magical hygiene routine. Early on, it was a teaching tool, showing me how to regulate energy in my body, sharpening my visualization abilities, bringing me to a beginning understanding of angels, and helping me control the spiritual elements. It can do all these things while making the local astral temporarily free of garbage energies / entities, improving energetic and physical circulation (like active meditation), and magnifying the will. Not bad for a single ritual, eh?
I also always recommend Peregrin Wildoak's By Names and Images: Bringing the Golden Dawn to Life as an indispensable handbook for these basic rituals. Wildoak talks about them in terms of the flow of energy, meaning, and spirit, giving you a very clear picture of what actually happens (or could happen). If you are a fan of Frater UD's "Models of Magic," you will recognize all those approaches in this book. It is the best way to understand the foundational GD rituals.