The texts of meditation are ideas, not thoughts, because thoughts arise spontaneously and are not governed by any visible law.
Ideas are set and fixed, and they are like seeds planted in the mind. When we meditate, we take an idea, and it has a two-fold benefit:
(1) it comes from a source which is enlightened, and its meaning is very exalting,
(2) it has he blessing of the enlightened source.
Then, meditation is an idea and it is to be planted deep, the mind is a field in which you can plant ideas, and therefore the meditation, which is an idea, is to be planted in the mind and held n the mind. The process is twofold. First, to make room for the idea by suppressing desires. Our mind is very often choked with desires; to “make room” means to suppress the desires by telling the mind that they are useless, that their conception does not lead to any real good. Then secondly, to exercise the power of the will to plant the idea and to hold it there. To hold it, it is helpful to use a key-word, into which all meditation condenses. Take “OM”. Every meditation begins and ends with OM.
A meditation is chosen, for example the Holy Gayatri. All that is highest and conducive to spiritual happiness is contained in this meditation. In the Holy Gayatri the key-word according to Swami Vidyaranya is Savitur meaning “the illuminator”.
“O Thou who art the illuminator, without Thee everything in this world is dark, limited, full of suffering; therefore it becomes effulgent only when Thy illumination falls upon it.”
Take this key-word. Think that it is written on the heart or between the eyebrows, and that you are reading it.
If any other thought arises, say to it “Savitur”, that it is not self-effulgent.
No thought is self- effulgent. The light comes not from the mind but from the power behind the mind.
So if in the meantime any thought arises, banish it by saying the key-word Savitur .
There is a way of meditation on “OM” given by Shri Sureshvara Acharya and Sadhu Nischal Das. The meaning of OM is elaborated in the “Mandukya Upanishad”.