How to Pretend to Look Surprised

We've all looked in our parent's closets and found out that they were getting you that gift you've always wanted. You also have an idea that they are making you a surprise birthday party. You have to show that you are surprised, so even if you know about it, learn how to look surprised.

Remember not to walk in fidgety and scared. This will give all of your planning away.
Think about all the other presents you're going to receive to take your mind off your parent's gift. Like, "I wonder if ____ got me that ____ I wanted? I hope so." Lose yourself in your thoughts and space out so when you walk in and everyone yells "Surprise!" or you open the present, instead of looking bored, like, "Oh, I knew this was coming" you will actually BE naturally surprised.
Know that when the time comes to open the present, pretend you're in a movie, or picture the present as something else. Like, a very expensive thing you know your parents would never buy you.
Understand that when you see the present, scream or open your mouth or look speechless. Say things gushing with gratitude but not TOO gushing, if you don't say "thanks" after every present and you suddenly say, "Oh, thank you thank you thank you thank you!" it will seem suspicious. Say Thanks after every gift so saying a small exaggerated "Thanks" after the present you know about will not seem strange.

Smile wide when you see the surprise party.
Look amazed when you notice the gift. But DON'T point it out if you know which one it is.