Being inconspicuous takes practice, skill and cunning. Here are some things that I've learned about staying anonymous.
Step 1: Dress for Success
Dress so you don't stand out. Normally this means dressing plainly. Although, sometimes you may need to dress up like a zombie to blend in with a crowd.
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
Don't behave in a way that draws attention to yourself. Don't scream and jump around. Also, don't act suspicious and keep looking over your shoulder.
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
Wear something to disguise your natural features without drawing attention to yourself. It could be as simple as carefully selecting a hat.
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.
Step 4: Stay in the Middle
Stay as close to the most dense part of the crowd. It is easier to find people straggling about on the edges. It's harder to find people that are in the middle of everything since everyone is moving around you. If people are moving in small groups through the crowd, pick a random one and pretend that you are with them by following closely behind.