The more simplistic the better. The less doctrine/guidelines to follow I believe will lead to a more open-minded religion.
For example. Instead of a list of rules or dogma to live by, instead just make sure your followers know: They are children of the earth, and consequently should treat both her and her children with respect. Going beyond that, we should always help others when we can, to lend a hand in order to mend the wounds humanity has inflicted upon itself.
You don't really need a religion to have good morales. I think that belief is what has chained many to religious teachings. They feel without it, they can't be good people. If I was ever the leader of a religion, I would want my teachings to be similar to Buddha's. He believed everyone had the potential to be as wise as he was, and that was truly open and loving. Kill the ego, feed the soul!