Tips: Go first thing in the morning or later in the afternoon/evening. It's busier in the morning, but that increases your chances of getting in w/o difficulty.
Try doing the Ollivander's show FIRST, if the line isn't too long. The line for that quickly grows to 45 min and stays that way most of the day.
If you have bags/loose items, do NOT enter the Forbidden Journey ride through the main castle. Go to the right and through Filch's (ride exit). Stay to the left and you'll reach the lockers. This area will be packed, but you won't have to wait in the Locker Line (which takes even longer!). After using the lockers, continue left and into the dungeon/queue. From there you can either go through the regular line, singles line, or Castle Tour line.
If you don't mind splitting from your group, use the single riders line at FJ. It's on the far left of the entrance, up some stairs. There is a small sign by it. If you reach the mirror of Eresid, you're not in the singles line!
The best place to get butterbeer is the Hog's Head pub. Enter through the walkway by the Gringott's ATM (near the restrooms) and enter through the door there. This usually has the shortest line.
A good viewing area for the Frog Choir and the Spirit Rally is in the Dragon Challenge queue. There is an area where you can easily step to the side (so DC riders can continue on) and watch from an elevated area.
A lot of the merchandise you find at WWOHP can be found at the Island Trading Company (huge store near the front of IOA) or the Universal Studios Store (near front of USF; near BMG and Rockit)
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