Close your eyes gently. Sit relaxed but alert. Silently, interiorly, begin to say a single word. It is utterly simple. Four equally stressed syllables.
Some people say the word in conjunction with their breathing.
The speed at which you say the word should be fairly slow, fairly rhythmical. Maranatha is in the Aramaic language Jesus himself spoke. It is probably the most ancient Christian prayer. St. Paul ends Corinthians with it, and St. John ends the book of revelation with it. Listen to the mantra as you say it gently but continuously.