Summarize:

Clean your hands thoroughly. Make sure that you wipe off every speck of dirt. You don't want end up getting sick because of this! You're going to be sticking your hands in your mouth. Therefore, try to make sure you don't have any type of residue on your fingers. Twist your hand and turn your palm away from your face. Your thumb should be pointed downwards and tilted away from your face. Make a hook shape by curling your index finger. One way to make this shape is to pick up a bag with one finger. Your finger will naturally make a curve.Without this hook shape, it will be difficult to make a noise. If this is too difficult to do with an index finger, you can try using your other fingers. Some people even use their thumbs to make this noise. Get a glass of water and drink it. This will ensure that your lips aren't too dry. Putting more moisture on your lips will make it easier to make a pop sound. You can use chap-stick or lip balm as well. You want to prevent dryness at all costs. Parched lips can be split quite easily! To do this, attempt to pronounce a word like toot or fruit. This is a good way to get your lips in the right place.The "o" shape should be big enough for your finger. Tighten your muscles. Make sure that your mouth and cheek muscles are taut. You shouldn't be able to move them around too easily. Place your finger gently in your mouth. You want to try to push toward the inside of your cheek. Don't stick your finger in too far! Tighten your lips around your finger. Keep a hold on your finger with your lips. Keep the position. Try to keep your lips in the same place. If you start to tire, stop for a moment. If your mouth position is incorrect, then it will be hard to make a sound. You may want to practice this before you start to do the trick. A good way to maintain this posture is to pretend that you are holding something inside your mouth already. Yank your finger out of your mouth. Be careful not to do this too quickly. You don't want to hurt yourself! You may have to do this a few times before a sound is produced. If no sound is coming out, try blowing out of your mouth while you do this.
Wash your hands. Create a hook-shape with your finger. Lubricate your lips. Create an "O" with your lips. Put your finger in your mouth. Wrap your lips around your finger. Pull out your finger.