Being present in the spiritual life always has a double meaning. There's present, as in here, in attendance. And there's present, as in now, a moment of time. What is the spiritual practice of being present? Being here now.
The world's religions all recommend living in the moment with full awareness. Zen Buddhism especially is known for its emphasis on "nowness." Hindu, Taoist, Jewish, Moslem, Christian, and other teachers urge us to make the most of every day as an opportunity that will not come to us again.
Also under the rubric of being present is the traditional spiritual exercise called practicing the presence of God. This means recognizing that God is here now moving through our everyday activities, no matter how trivial they might seem.
Why This Practice May Be For You
The contrasts to being present are living in the past and living in the future. We do the former when we hold on to regrets. We constantly review things that have already happened, trying to explain them in terms of our own or someone else's actions. Often this kind of thinking leads to guilt or blaming.
We live in the future when we make assumptions or fantasize about what could happen and then become attached to those expected outcomes. This habit usually results in disappointment. Whether we are consumed with positive expectations (optimism) or negative projections (pessimism), we are not living in the moment.
When you find yourself constantly reacting to your experiences in one of these ways, when you always want to be otherwise and elsewhere, it is time to be present. The companion of this practice is contentment.