Smile and Make Eye Contact
Smiling at someone lets him know you like him without being intimidating or overbearing. So relax, make eye contact, and then flash a grin. Then look back at whatever you were previously focusing on: a friend you were talking to, a book you're reading, a movie you're watching. You don't want to stare at the other person for too long; that can be awkward.
When speaking to the person you want to flirt with, make sure you ask him questions. Ask about the hobbies or sports he's into, or what he thinks of the quiz in math class. This is a subtle way to show you're interested in getting to know your crush better.
While you're finding out more about your potential date by asking questions, don't forget to play up your own strengths. Killer soccer goalie? Find a way to mention it. Math class superstar? Don't act like you're not because you think smart girls can't get dates. You'll be more appealing if you show where you shine.
Give Some Space
While you might be tempted to text your crush between every class or call him right when you get home, this behavior can actually have the opposite of the intended result. You might overwhelm the person you're flirting with and turn him off. So if you've already shown your interest, let him make the next move.
Know Who You're Flirting With
Flirting with someone your own age who you know from school, your religious place of worship, or your sports league can be a lot of fun. Flirting with anyone older than you or that you met online is a bad idea and could be dangerous.
Complimenting your crush, along with asking questions, is a great way to let him know you're interested. If you notice his play performance or stellar guitar-playing skills, let him know!
Approach Your Crush Yourself
Tweens often let someone else deliver the message that they're interested in someone. This is a bad strategy, because it makes you look less than confident. Do the flirting yourself and you'll have better results!