Summarize:

You'll need someone to perform your magic trick for. Search out a group of people to amaze. Look for people who seem friendly and open to your performance. Avoid people who seem reclusive or groups in the middle of serious conversation. Be sure to smile warmly so they feel relaxed in your presence. When addressing a group, position yourself so everyone can see you. Speak loudly enough for them to hear you. Make eye contact as you talk. Politely tell your audience that you'd like to perform a magic trick for them. Tell them you'll need a volunteer. Learn the relationship between the people in your crowd. If they're coworkers, you'll likely want to pick the boss. Confident people tend to make better volunteers and will play along to entertain their employees. Find out your volunteer's name and introduce her to the crowd to make her feel like part of the show. Say "This is Anna (her name), and she'll be helping me perform today." Be firm when choosing a volunteer. Point at them and say "I want you to help me." Don't give them a chance to say no or the rest of the audience will think they can say no as well. Say "As you can see, these are in no particular order." Sneak a peek at the last card in the fan. That's the card you'll be forcing on your volunteer. Shuffle the cards a few more times but be sure to keep the force card last in the fan. With your cards fanned out face up, the force card will be at the bottom. Remember your force card, it's the card you'll be making your volunteer choose later on. Flip it over so that the cards are now facing down. The force card is now the top card in the deck. Now that you know the position of your force card, you're ready to perform the force.
Find your audience. Approach your audience confidently and introduce yourself. Pick a volunteer. Fan the cards. Reform the deck.