Mindfulness has become a buzzword in modern culture, and is an frequently misunderstood concept. A common misconception about mindfulness is the idea that you have to be "in the moment" all the time. Many people (formerly myself included) find this idea so inaccessible that they become turned off to the concept as something that they could never do, therefore they never try.
Basic mindfulness is as simple as noticing as a curious observer to the present moment. This can be practiced in our external world (noticing through our senses anything outside of us) or in the internal world (observing our thoughts, emotions, physical sensations, behaviors.) Engaging in the art of attention is powerful in that we can steer our attention away from our usual mind chatter towards anything else, internally or externally.
To begin, start with external objects to be mindful of. Notice things in your environments, sounds, sights, smells, textures. When your mind drifts, which you should expect, notice the drift, and return your mind to the object you are being mindful of. Expect your mind to wander, and try to nonjudgmentally return your attention. If you get stuck in the thought that you are bad at mindfulness, you are less likely to try again. This thought "I am bad at this" is a thought to be unmindful of - pay it no attention and simply return your attention. In practicing mindfulness of something in our external world, that object serves as an anchor to hold us in the present.
Mindfullness is not how long you are in the moment, moreso, noticing when you are not present and returning to the moment you are in. You may return your attention many, many times in an hour, but the process of noticing your are drifting indicates greater mastery over the ability to steer your mind towards where you want it to go, rather than where it goes on its own.
In my work, I find that the people that have the most success at reducing unwanted thoughts and anxieties are the people that are most mindful of their thought patterns. Mindfulness is the foundation to all behavior change, as, if you are not mindful of what you are doing, there is very little ability to change how you are dong it.