"How to do it?"
I’ll keep this short and sweet. Find a comfortable, distraction free space. You can sit upright on a chair or on a pillow on the floor. Don’t lay on your back - that cues the body for sleep.
Think ‘sit with dignity’. Sitting with dignity is right in the centre of two outliers: big, bold and broad body posture (think of an athlete in a confident, winning stance or a superhero-esque pose ) and the ‘ihunch’; a contorted position you see many in while walking the streets with their mobile phone - head tilted forward, shoulders small and rounded. Your sweet spot is in the middle of those. Not too bold, not too contorted.
Okay, now you must find your anchor. Your anchor is the very thing you’re going to use to bring your awareness back when you drift off. And you will, this is totally normal.
The most common anchor is breath. You can either use the 627 formula - breathe in for 6, hold for 2, exhale for 7 - or a mantra, such as release, said repeatedly, over and over. When you drift off, bring yourself gently back to either your mantra or the 627 formula time and time again. Set a timer for 5,10 or 15 minutes and begin. And don’t feel like you have to experience some magical sensation or that you’re cleansed of all of life's ills when complete. Just like it takes time to strengthen physical muscles, it also takes time to strengthen mental muscles.