To achieve Gnosis, one must find his/her truth, while disregarding outside influences, for truth is perception, and all is mental.
Once you have done so, you have no one to ask but yourself. And in time, with experience and knowledge, one will seek out, through his/her truth, a desired representation, symbol, archetype, or god, to aid in ritual act.
This exercise is just another way in which you can obtain gnosis, and is the basic intent. You may however use it as a "mental preparation" for ritual.
I would recommend for the meditation that you lie down in a dark room with silence. Use familiar scents such as incense, and never change the scents. You don't want to confuse or use different things while doing what I call "mind work". You may begin to feel confused or such due to new things presented in your atmosphere.
Find a seat or lay down. Make yourself comfortable and begin meditation. Once you are comfortable and focused, take yourself to any general place in your mind and watch it deteriorate, so that you are now surrounded by nothing.
Let no words, actions or ideals come into your mind other than that which you create and examine yourself. (This is, how I would put, a "key" to the inner self. The disengagement of worldly views or outside influences). Nothing can, or will effect you in any way. You are one, in a timeless void. The only thing that can and will exist inside this nothingness is your mental manifestation of your will or you yourself, your being. You are now beyond the fabric of worldly influences.
Step out of thevoid/nothingness(open your eyes), and begin your ritual, if ritual work is desired at this point.
It would be wise not to force anything during meditation. It takes practice. After this particular exercise, I like to just let the mind wander, asking myself questions or analyzing anything at all.
If Ritual is desired:
Any incense, candles, symbols, weapons, etc., may be used, for of course, magic is that of intent. Color is metaphor, and symbol's meanings are that of the individuals perception.
Any ritual will work with this exercise, whether it be invocation, evocation, banishing, or any other spell, or magical act. And can also be used for any symbol, archetype or god, including yourself. You can end the ritual by stepping back into nothingness, and returning, by doing meditation backwards.
Although I will state again that for the most part this is not a ritual in itself, but can be used for preparation. I would call it a state of mind and key to gnosis.