Get ready to notice when you start thinking.
Don’t breathe forcefully or change your breathing in any way. Simply observe it; notice the air flowing in and out of your nose and touching your upper lip. Feel your chest and belly rising and falling. If you like, count your breath cycles until you reach 10, then start again. If your attention slips, start over at 1.
Pick a simple mantra that (e.g. “One” or “Omm”). Your mantra is a word that you should not have too many associations with, as this would engage your mind too much and be counterproductive. Visualize/Imagine the mantra gently floating towards and over you again and again, like a wave in the ocean or a leaf in the wind.
Don’t do or focus on anything. Simply observe whatever comes to your attention in that moment – a smell, a certain feeling, a thought, an itch, a sound. Stay very mindful. If you notice your attention slipping, bring it back to an anchor (such as a sound or your breath) for just a moment, before you again let go of that focus.