An average of over 50% scroll would be a good place to start. You have created a whole page, to deliver value for the user, ideally the average person is consuming at least half of it.
You do need to be mindful of where calls to action are, as they can pull people away, which is a good thing but it does impact the metric. Be mindful of load times, or high bounce rates, as these can also reduce scroll.
This is part of our Guide to Scroll Depth.