There is no effort that we can make to still ourselves. True stillness comes naturally from moments of solitude where we allow our minds to settle. Just as water seeks its own level, the mind will gravitate toward the holy. Muddy water will become clear if allowed to stand undisturbed, and so too will the mind become clear if it is allowed to be still.
At the extremity of prayer words vanish, or rather the "silence-become-word" surpasses all that can be uttered. Prayer becomes the silence of Love, and this silence reveals the "I" in its deepest aspects; and, should words suddenly arise in prayer, we must regard them as fruits of love that send us back to silence.