Step 1: Dress for success
Anticipate what the rest of the crowd will look like and use common sense. Avoid bright colors or revealing clothing. Avoid anything that could get people to pay attention to you. Avoid being too out of style and too in style. Avoid things with big logos or graphics on it.
In most situations the ideal outfit has dark muted colors, is clean, covers your naughty bits and matches. It should have a timeless look.
Step 2: Don't draw attention to yourself
Use common sense. Behave the same exact way everyone else is behaving. If everyone is screaming and jumping around, then do the same.
Step 3: Wear a disguise
You would be amazed how hard it is to find someone you know in a crowd that is wearing a hat that you've never seen before.
Changing the way you walk is also surprisingly effective. You can remove the liner from your shoe to walk lopsided or if you don't mind pain, just put some rocks in a shoe.