One way to become a good liar is to take an acting class or to sign up for a theater production. Actors are, in a sense, professional liars - good actors use their faces, voices, and bodies to weave a convincing story.
There’s a reason it’s called a “poker face” - to help develop stone-cold control over your facial expression, get together with friends to play a little Texas Hold’Em or another poker variation, most of which encourage players to hide their emotions.
If you’re sneaking around people who don’t know you, you can pre-plan your excuse to the extent of having a fake name and/or backstory. Support your story with your choice of wardrobe and demeanor - if you’re pretending to be a religious missionary, for instance, you might want to wear clean slacks, a white button-down shirt, and a tie (if you’re male) and to carry religious literature with you.
If you’re really brave, you can even create a disguise and pretend to be someone you’re not - keep in mind that impersonating a police officer, etc. is a serious crime!
In the example scenario, be sure to keep up your façade until after he’s been surprised! If you give into giggles even a few seconds too soon, you could give the surprise away.
If you have a chance, study the location you’re going to sneak around in and the people you’ll encounter. Take notes. Even consider sketching simple maps - these will help you plan a strategy for sneaking around this place and getting around these people. Look for patterns in peoples’ behavior. For example, if you see that your friend gets home from work at 6 PM every day, you’ll know to have your prank set up before then.
If someone’s talking on a phone on a land line, try picking up another phone on the same line to overhear easily their conversation from another part of the house. Just be sure to do it very, very quietly - don’t breathe into the receiver.
Avoid large, open areas. You can’t see in every direction at once, so in these areas it’s hard to keep track of other people and, thus, easier to get spotted. Stay near walls when possible - you know you can’t be seen through the wall, so you can focus your attention on the angles from which you’re more likely to be spotted. If you can, learn a building’s floor plan before hand. Even a basic understanding of where most of the rooms, windows, and doors are located can help you make good choices about which areas to avoid and where to hide if the need arises.
Walk with delicate steps. Keep your knees slightly bent as you shift your weight slowly from one foot to the next. Use a gentle heel-toe step. Wear quiet clothing. Don’t wear clothes that make noise when they’re ruffled or when you move in them. Soft fabrics are best - sweatpants and many types of athletic wear work well. Wear soft footwear. If you must use shoes, wear a pair with soft soles that won’t squeak on wet surfaces. Slippers are better. Bare socks are better still! Don’t touch noisy surfaces. Most carpets are quieter than hardwood floors, which can squeak and amplify the sound of your footsteps. Also, avoid bumping into any glass or metal or stepping on twigs if you’re outdoors. If possible, make significant movements only when there’s another noise to cover it up (for instance, when an airplane flies overhead).
When trying to avoid conversation, try to look like you have something to do. Walk with purpose - like you’re on your way to something important and can’t be bothered to talk.
Pickpockets use misdirection to steal wallets - you can use the same principle to sneakily mess with your friends! Keep your friend’s attention focused on one thing - a funny video or a card trick, for example - while you stretch one hand out of their line of sight to snatch what you want.
If you haven’t already, start a well-balanced exercise routine to start on the path to personal fitness.
Try this sneaking exercise: While sitting in the passenger seat, see if there are any coins in the cup holder. Slowly but surely, (over the course of the car ride) take the coins out one at a time. Be sure the driver is not watching you, and try not to make any noise. Later, try to place all the coins back in the cup holder. This exercise will improve your hand steadiness, your ability to move silently, and your ability to read the body language of people you’re sneaking on!
Try this exercise: at a social event, watch someone who has a drink out of the corner of your eye. Wait until their back is turned, and then move the drink to another room. After you have moved the drink, go back and watch them as they try to remember where they put it. Make sure you keep a straight face - don’t give away that you had something to do with it. This exercise improves your ability to keep inconspicuous in crowded areas as well as your ability to control your emotions in the face of someone you’ve duped. For a good test of your ability to move silently, stay awake late at night and try to move around the house silently when everyone’s asleep - pick a point in your house to sneak to, then sneak back to your room, going through as many rooms as possible. In the stillness of the night, you’ll be able to hear even smallest movements.
Some people have a visceral negative reaction when they tell a lie that is detectable by others. To start getting over this, begin by telling inconsequential, harmless lies. When someone asks for the time, tell them it’s one minute later than it is. You’ll eventually work through your reluctance and, if you gradually scale up your lies, soon you’ll be able to tell convincingly “real,” consequential lies. If you’re not socially squeamish, try talking your way into a members-only gym or country club as a good test of your social sneaking abilities. Craft a good excuse beforehand - maybe you left your wallet in the locker room, or maybe your friends are inside waiting for you but they can’t let you in because they’re in the pool away from their phones!
