There is no progress in prayer without progress in faith, a purification of faith. And this entails the removal of all the props which depend on human endeavor, human reasoning, signs and the rest. It is the naked faith which is a terrifying experience and yet is the meeting point ultimately between God and ourselves in the depth of our being. This experience of the purification of faith is not normally one which comes early in the spiritual life. We must learn to wait.
Dom Henri le Saux, a French Benedictine monk, suggests that the sacred sound "OM" can be used by anyone:
More than any particular name of Divinity, OM conveys the ineffability and the depths of the divine Mystery. It bears no distinct meaning ... It does not even recall any mythological or semi-historic event. It is a kind of inarticulate exclamation uttered when you are confronted with the Presence in yourself and around yourself.
You could say that OM is a name of God which is not a name.