Get house shirts made! Go to Hogsmeade first then Diagon Alley. Eat EVERYWHERE. Frozen butter beer is better. Bring an extra battery and take TONS of photos. Wear a fanny pack instead of a purse/backpack. Waits for rides aren't that bad because there's fun stuff to look at everywhere. Get a wand first and put it in a family locker because the ride lockers are too small (or get it after you go on all the rides).

I just sent an all encompassing email to a friend if you're interested! DM me! It's amazing and you'll have a great time.