Silence is a difficult discipline--the most difficult for me, anyway. There are various ways to approach "centering down" as Quakers say. I borrow from other traditions as needed.
One is to think of a saying, in "lectio divina" style: an example is the verse, "Be still and know that I am God." ... wait with it for a few moments. "Be still and know that I am." Wait.... "Be still and know." Wait.... "Be still." Wait.... "Be." Wait.... "Be still and know that I am God."
Or use a single word, whatever you feel you need most at the time.
Another is to observe your breathing--just pay attention to it.
Or hold people in the Light (a.k.a. praying for them, in whatever fashion works for you). Sometimes I start with the people in the circle, then expand it. When I get to the whole world, that's as centered as I get! If I get that far, and "come back to myself" that often seems to correspond to others' sense of a "gathered" or "covered" meeting -- when we are communally filled with the Spirit.
There are many books, pamphlets, & blog posts for those who want to read more.