Say the Jesus prayer by St Joseph the Hesychast

Say the prayer “Lord Jesus Christ, have mercy on me” with your tongue and with the nous without ceasing. When the tongue becomes tired let the nous begin. And again, when the nous is burdened, the tongue. Just do not stop. Make many prostrations; keep vigil at night as much as you can... So then, when praying occupies his nous he imagines nothing, but pays attention only to the words of the prayer.
Saint Joseph the Hesychast