The LBRP, the Lesser Banishing Ritual of the Pentagram has several forms. My favorite comes from FutureRitual by Philip H. Farber, with a little help from http://www.digital-brilliance.com/kab/faq.htm#LRBP It has been used as a way to focus one's mind before performing a more complicated ritual, or for banishing outside influences before meditation, or in the Jewish Religion as a bedtime preparation.

The ritual seems to be just as effectual performed IRL or astrally (in ones mind alone).

I know of 3 versions of the ritual,and there are probably many more.

It starts with the Qabalistic Cross:
Stand facing East. Visualize yourself in magickal garb. Visualize your life force as a light at your solar plexus. Visualize a circle drawn around you, big enough that if you rotated it around the center (where you are standing) it would pass about a foot over the top of your head. Visualize that it is indeed a sphere, surrounding you, containing your energy and blocking out any external energy.
Expand your light by will alone to permeate and fill this sphere.
Reach up and touch the crown of your head with your finger or wand (this is astral, it can be anything!) and intone ATEH (sounds like ah-tech with a very soft ch). An intonation should take an entire deep breath.
Visualize an extremely bright light from infinity coming down upon your head.
Move your wand down to touch the base of your spine, visualize the light flowing down along your spine then down to infinity, intone MALKUTH (short a long u hard t then a soft breath).
Touch your right shoulder with your wand, imagine a very bright light from infinity coming to your right shoulder intone VE GEBURAH (short e's soft b almost a v long u short a very soft ch).
Draw your wand across to your left shoulder, the light flowing through your chest to the left shoulder then off to infinity, intone VE GEDULAH.
Clasp your hands at the point where the beams cross, intone LA OLAM.
Bow your head, intone AMEN (Ah Men not AY men).
(end of Qabalistic Cross)

In the East, draw a 3 foot tall pentagram, point up, on the sphere (I like blue flame), at eye level. Start at the bottom left, up to the top, down to bottom right, up to left arm across to right sown to start. Stab your wand at the pentagram and visualize it flashing brilliantly, intone YOD HE VAU HE (just like above, AU sounds like OW in COW).
Turn to your right, the south, visualize a line of flame (I like blue) following the arc of the sphere at eye level, here draw another pentagram the same way, stab, flash, intone ADONAI (AI sounds like eye).
Turn to your right, the west, same line, same pentagram, stab, flash, intone EHEIEH (eh heh eee eh).
Turn to your right, the north, same line, same pentagram, stab, flash, intone AGALA.
Turn to right, complete the circle.
Hold your arms out like a cross, facing east, say the following, intoning the names in caps:
"Before me RAPHAEL ( rah f-eye el, visualize a yellow wind blowing into the sphere and filling it.)
Behind me GABRIEL (gah bree el, visualize blue water from the west flowing into the sphere)
On my right hand MICHAEL (mee kha el, visualize red fire from the south roaring into the sphere.)
On my left hand AURIEL (ow ree el, visualize olive green earth rolling into the sphere from the north.)
For before me flames the pentagram (visualize all your pentagrams glowing with renewed vigor, plus a fifth one on your chest)
and in the column shines the 6 rayed star!" (visualise a 6 pointed star in your spine at heart level)

(repeat the Qabalistic Cross)
(commence meditation) (close the circle) (go about your new existence)

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