One thing I am noticing is that there is less and less uniformity in our Anglican congregations over what we do with our bodies in worship. Standing for the gospel reading in a Communion service, for example, is no longer uniform. The situation is not helped by options being allowed by prayer book rubric: for example congregations may sit or stand for the eucharistic prayer.
I suggest worship leaders should themselves be clear about the what and why of body posture in worship. Without this clarity leaders may forget to ask people to stand, sit, or kneel as appropriate for a particular part of the service.
The principles are fairly straightforward.
We stand to make declarations of truth, praise and thanksgiving.
We stand in order to honour God.
We kneel to symbolise our humility.
We sit to listen.
Thus we stand for the creed, to sing songs and hymns, and for the eucharistic prayer.* We also stand at the beginning of the service to honour God at the beginning of this consecrated time of worship, and for the gospel reading to honour our Lord who is the subject and centre of the Gospel.
Then we kneel to confess our sins and to make our intercessions; also to receive the nourishment of God through the bread and the wine.
Pretty much every other part of the service involves us listening (readings, sermon, notices), so we sit for these parts.
*As a concession to infirmity we may sit as an alternative kneeling; and we might change from standing to sitting in the middle of the eucharistic prayer.