Living in the moment: It is the basis of a whole philosophical movement. Almost every spiritual practice embraces it. It is both simplistic and complex in concept; living in the moment is about just being. Being fully present in every situation, body, mind, and soul, so that you experience everything you do totally and absolutely. In those moments when you engage yourself completely, nothing in the future exists - and nothing in the past is holding you back. While it might be a challenge to always be present, you can start small.
As you go about your day, try to be aware of what you're doing, be it driving, typing, or even drinking water. Give your full attention to each activity. As often as you can, pay complete attention to everything in your immediate surroundings, and keep your thoughts to the moment at hand. Set aside your anxieties about next week's meeting or tomorrow's dental appointment. Spend your energy on the awareness of your breath, your muscles when you walk, the texture and smell of what you eat or drink. Listen intently to every conversation, without any expectations, without finishing anyone else's sentences, without preparing your rebuttal.
Even everyday chores warrant your full focus, whether you're writing a dissertation or washing dishes. Be aware of your surroundings. Notice the color of flowers, the scent of rain, even the gum on the sidewalk. Pay attention to what is happening at every moment, but don't fight what is. Accept that there is a long line at the post office, but don't let it upset you. After all, there's nothing you can do about it anyway. By simply accepting each moment as if you have chosen it, you'll be surprised at what the day has to offer you. Perhaps that time on the post office line will offer a moment of mediation, a lesson in patience, or an enjoyable session of people watching.
You'll find that by living in the moment, you'll be calmer, probably more productive, and most importantly, more content with life.