Skateboarding help: ollies?

I can ollie but not to consistent and sometimes the nose of the board does a nosedive. I put my backfoot with my big toe and the toe next to it on the tail and with the rest of my toes off the edge to snap it down, should I have my whole foot on the tail? and my front? should I have some heel hanging off wit my toes even to the edge of the board? Or should I have my foot centered wit some toe and some heel hanging off? Or is it all personal preference? I want to land them cleaner and more consistent please help thank you