Here's a re-post from a few years ago that I thought would bear repeating:
If you're constantly thinking about what you'd rather be doing—getting off work, driving a different car, or eating dessert, your mind is starving for mindfulness. So what? Well, if you're reading an instant message and talking on your cell phone while thinking about things you need to get at the store, you're not doing any of these things fully—and essentially, you're missing out on your own life.
The antidote? Mindfulness. Mindfulness is a quality you can cultivate in any situation—whether you're walking down the street or washing the dishes... In mindfulness meditation you stop the restlessness of your mind by focusing your undivided attention on whatever you're experiencing in the here and now. The simplest version involves simply focusing on your breath. By enhancing your awareness in this way, you calm your mind, experience life more fully, and bring new clarity of thought to any situation that comes your way.