It can happen anywhere. You're walking along and—bam!—celebrity sighting. Save yourself from embarrassment and follow these nine tips.

1. Don't scream.

No matter how excited you might be, do not scream. Screaming in someone's face is no way to properly greet anyone.

Example 1: When waiting for One Direction, the fans outside The W Hotel in Beverly Hills were challenged to stay quiet as the band walked outside. Apparently this is hard to do, because the second Harry Styles' signature locks walked through the glass doors, the girls broke into a screaming stampede. Ladies, if you stayed calm, they may have been able to meet all of us. Lesson learned.

2. Don't take a picture of them without asking.

If Cole Sprouse's Instagram is any indication, celebrities do not like random people taking pictures of them without their approval. In certain situations, celebrities are prepared to face the media. These include concerts, meet-and-greets, promotional events, and public interviews. If your favorite celebrity is enjoying a nice lunch with friends and family, don't try to sneak a picture of them. This is creepy, and you're not as sneaky as you think.

Example 2: When I saw Julia Roberts at the St. Regis Hotel, my dad tried to take a picture of her by raising his phone over his head. My mom quickly pulled his arm down. Be cool, dad, be cool.

3. Try not to interrupt.

You can usually tell if someone doesn't want to be interrupted. They're trying to be incognito, they're in a hurry, or they're deep in conversation. However, if you absolutely need a picture and the celeb is otherwise occupied, politely say, "Excuse me, but I'm a huge fan. Can I get a picture with you?" Usually they'll be nice about it, but be prepared for rejection.

Example 3: When Lorde walked by me and my parents at The Kettle in Manhattan Beach, I said "Excuse me, Lorde?" She didn't look up, or acknowledge that I said anything. I got ignored by Lorde.

4. Only ask for one picture.

Celebrities are busy people, and they don't have time to take the same picture over and over again until it's Instagram perfection. Again, only ask if you really need a picture with this person.

Example 4: I met Chris Pratt at a hotel on Sunset and I absolutely needed a picture with him. The first picture we took had major sun glare, so he suggested we take another. It looks like he's pulling my hair in the second picture, but we weren't trying to start a photo shoot in the middle of the lobby.

5. Gauge their reaction.

Sometimes it's harder to tell that a celebrity doesn't want to be bothered. If you end up talking to them, look at how they respond (or don't respond). If they look distant or uncomfortable, say "Sorry for bothering you. Have a nice day," and leave.

Example 5: Hannah Simone, Cece from "New Girl," was having lunch at The Grove with a friend. When she noticed that everyone at my table recognized her, she quickly shifted her seating arrangement and it was obvious that she didn't want to be bothered. We all agreed not to go up to her.

6. Think before you speak.

You're probably nervous, so think about what you want to say to the celeb before you walk up to them. Thinking before you speak reduces the probability of awkward silences.

Example 6: I met Hayden Panettiere at a screening of "Bring it On: All or Nothing," and couldn't think of anything to say."Save the cheerleader, save the world?"

7. Remember that they're people too.

When it comes down to it, celebrities are just people. It's easy to idolize them, but the more you think of your #1 bae as a regular person, the easier it will be to approach them in real life if you ever get the chance.

Example 7: As a life-long Harry Potter fan, I was ecstatic when I met Tom Felton at the Shrine Auditorium. Once I talked to him for a few minutes, I realized that he's down-to-earth and we joked about playing Muggle Quidditch.

8. Know their name.

This seems like a given, but there's always that one celebrity that you know you know from somewhere, but you can't pinpoint exactly where they're from or their name. Don't go up to a celebrity and say, "Hey, you're that guy from that one show, right?" This makes everyone uncomfortable.

Example 8: At the Grove farmer's market, I ate lunch next to J.K. Simmons weeks before he won an Oscar for Best Supporting Actor, but I couldn't remember his name. It wasn't until hours later that I was able to Google my way to the answer. This interaction would have been embarrassing if I had tried to talk to him without knowing his name. (Sorry J.K., you were great in Spider-Man.)

9. Think about where you are.

Sometimes you'll run into celebrities in unexpected places. If you're in a professional environment, be sure to keep that in mind.

Example 9: Miraculously, I ran into Chris Pratt a second time within a month of meeting him. I was in the parking structure at my internship, so I knew I had to be extra professional. After I looked back and forth between my picture with him on my phone background and the real Chris Pratt in front of me, I said "Hi." He said, "Hi, how's it going?" and I said "Good." Exciting stuff, right? I pretended to be super chill as I texted my mom: I JUST SAW CHRIS PRATT!!! I spent the rest of the day trying not to make this face:

Sometimes you'll run into celebrities when you least expect it. Follow these nine tips, and you'll be an expert at playing it cool.