1. If you are in line and they are asking for doubles, don't go. You'll get two elevator rights and a few bland hallways to look at before you get stuck in a room waiting for enough people to fill out the cart. Wait time is not expedited.
2. Stow your backpack, purse etc in lockers well before you get into the ride. The lockers within the ride are a PIA and its not unusual for them all to be taken which means you end up waiting additional minutes for a locker to open up.
3. The Ollivander line is brutal. Avoid it during the hottest parts of the day at all costs. Once you get into Ollivanders, plan on being shoulder to shoulder with other wand buyers. If you are not buying a wand, skip the entire thing. Not worth it.
4. What I found both times I was there 4th of July week was that there was NO line to get into Hogsmeade later in the day. If you tried mid to late morning or early afternoon though you could be in the Hogsmeade line for an hour and then have to spend another hour in the FJ line.
5. You can by chocolate frogs at the souvenier shop at the park exit, you don't need to haul them all over the park all day.
6. Once we were in Dumbledores office, it snowed. One time it didn't. I have no idea if there is a pattern to that or it was just a fluke.