I'll be able to give you some first hand experience after we get back in a couple weeks, but from what I've gathered, if you really want to see WWoHP, you need to take advantage of the early entry for onsite guests.
In our case, we'll be able to get in at 8, so we plan on leaving the resort at 7:30ish. It seems like they usually open a few minutes before and although everyone is heading to the same place, you have to imagine that it's a MUCH smaller crowd than when the gates open for the general public at 9.
My kids are a little young to be big HP fans, but our plan is to head straight to Forbidden Journey since my DD6 likes thrill rides. I've read that you should try to get into Olivander's first and the FJ before the park officially opens - they seem to be the most crowded as the day goes on.
I'll be sure to report on our early entry experience when we get back - we're so excited!