"The easiest way to form friendships would be through a common interest - whether that's at the gym, at a book club, or through a religious institution," says therapist Nicole Zangara, LCSW, author of Surviving Female Friendships: The Good, The Bad, and The Ugly. People tend to be friends with those who have similarities to them, including likes and dislikes, common interests, and even specific personality traits, according to a study published in the journal Psychological Science.

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Your body language matters. "Smile and make eye contact, as this can break the ice," says Stewart-Hyslop. Research published in the journal Motivation and Emotion found that smiling is key to forming new friendships, as people are more attune to positive emotions when they're forming new relationships.

"Rather than focusing on turning a stranger into a friend, focus on turning friendly acquaintances into friends," says executive coach Amy M. Gardner of Apochromatik over email. Research published in the journal Organization Science found that reconnecting with long lost people can lead to strong friendships, even if lots of time has passed without contact with them.

It might sound counterintuitive, but asking someone for a small favor can make someone like you more, according to research from the journal Human Relations. Asking for a favor can indicate intimacy and trust, and it can appear as an expression of esteem.

Use the exposure effect to your benefit: The more often you are exposed to someone, the more likely you are to like the person. "Without becoming a lurker, spend more time at a place where you like to hang out anyway," says Gardner. "The more you do, the more likely you are to be repeatedly exposed to people who have something in common with you."

"Whether you choose to volunteer at a food bank, walk dogs at a shelter, or join a museum’s junior board, volunteering can benefit the organization as well as you, in part by helping you connect to others who share a common interest and desire to improve their community," says Gardener. Studies show that volunteering can be a great way to form friendships and receive social support.

Vulnerability is one of the factors in creating intimacy with someone, and self-disclosure is a key ingredient in forming relationships, according to research found in the book Friendship Processes. "Self-disclosure is sharing personal information about yourself, when appropriate, with people you want to develop a closer relationship with," says psychologist Dr. Wyatt Fisher over email.

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Research published in the journal Physica A found that reciprocity — returning phone calls from a friend, for example — is the strongest factor in whether friendships last. "When a friend reaches out, respond," says Gardener. "When a friend needs you, be there. We get busy, and life, work, and the business of adulting can keep us from being a good friend."

Don't hold back when it comes to your humor. A study published in the journal Human Nature found that sharing a laugh with someone makes them more likely to share personal details about themselves. Laughter can help people feel more relaxed about the details they communicate, so don't be afraid to bust out your favorite joke.

"Make a genuine effort to get to know someone," says relationship expert Naomi J Hardy, CLC, MSTC over email. "It is easy to spot when someone is going through the motions of listening and just waiting for their turn to speak." Research form the Journal of Personality and Social Psychology found that people who ask lots of questions when getting to know someone are rated as more likable than those who ask fewer questions.

Having a pet can do more than just keep you company at home — it can help you make friends. People with dogs are more approachable and meet more people in general, according to multiple studies. If you aren't able to own a pet, consider becoming a dog sitter or dog walker.