Most religions and philosophies agree on some basic values that are in the ten commandments. Native American beliefs are often harmonious in basic ways to European and Asian beliefs and values. I think an invocation/prayer which attempts to focus people on basic, spiritual values is important and helps us rise above, if only momentarily, our own pettiness is helpful when trying to work together for the common good. Focusing upon what we have in common rather than on our differences is good medicine for a functioning democracy. An invocation that reminds us of our common values might be a good thing to have precede your assembly meetings.