For anyone with depression, anxiety, stress, frustration, ______________ (any other thing that keeps you from being calm and centered) the practice of mindfulness can be of great benefit. To add to the different offerings thus far, I offer this.
Mindfulness is being engaged in the present moment. You do not have to meditate to practice mindfulness. (It will help though). To put it another way Intention with Attention or one that my therapist told me.....make sure your feet and your mind are in the same place. Often times we tend to live in the past or fantasize about the future. Neither of which are where the individual actually is.
The book that I first read was "Wherever You Go There You Are" by John Kabat-Zinn. You can also find videos of talks that he has done on Youtube.
Things that you can do "check in" with yourself.... set a random alarm on your phone and when it goes off see if you were engaged in the present moment. You can also set hourly reminders to reset as needed. The important thing is to not be harsh on yourself, or be judgmental. See it rather as an opportunity to understand that the mind wanders, obsesses, and does its' own thing. When you start to see these things, you will notice patterns and seeing these patterns will then provide you with other areas to understand.
When mindfulness was first introduced to me in 2010 it seemed so foreign to me. Then I read that book(mentioned above), and I have never been the same. For me, the concept of mindfulness introduced me to mindfulness meditation (Vipassana to be exact) and then that changed my life for the better even more.
One of the things that I did early on was tried to catch myself throughout the day making snap judgements, doing things that I was unaware of, and take notice of where my mind took me when I wasn't in the present moment. The results were astounding.
So to answer your question my experience with Mindfulness has been amazing, rewarding, challenging, and eye-opening.
Kind Regards Shark