There are many magic tricks you can do with a cup. Here are two of them which you can practice and perform in front of your friends.
The first is called the Three Cup Shuffle Magic Trick. Here, you use a poker chip or large coin and guess where it is hidden. For you to tell where it is each time, you have to put a piece of invisible thread measuring about 3 to 4 inches long taped to it. You have to be sure that no one will see this and know what to look for when the cups are shuffled.
The trick begins by explaining to the audience that you can find the chip regardless of which cup they put it in. You then ask someone from the audience if anyone is willing to challenge you on that. (Chances are someone always does.)
Once you have a volunteer, let this person inspect the three identical cups and when it is finished, you place the chip over one cup and then let them shuffle as long as they like.
To create suspense, turn your back and only face them again when they are finished. You now look over the three cups searching for the invisible thread and when you find it, tap the cup so the volunteer will open it.
The second is called the Cup and Balls Trick. The objective here is to let all the balls pass through all the cups. For this, you will need three cups that are not see through, four identical balls and a wand.