You don’t need to make casual friends with your coworkers and hang out with them every weekend. But it can certainly help make the work week more manageable. Rather than “dealing with coworkers,” your workday begins to feel more like “hanging out with friends,” and that’s always a better option provided that you can still be productive together.
You already have more than enough common ground to form a solid friend relationship with the people you spend time with at work every day — after all, some sort of common interest or circumstance has you in the same line of work.
Accept invitations! Happy hour drinks after work, housewarming parties, all order of occasions such as these are opportunities for you to show up and demonstrate yourself as a friendly person worth knowing outside of a work context.
Learn about them, remember their interests. Just as you have a deep, complex inner life, so does everyone you work with. They have their own hobbies and extracurricular interests. With a little luck they might have some in common with you, or at least be able to tell you some really interesting details about their non-work pursuits.
Ask them questions based on things you’ve remembered. This is probably easiest when they return from a vacation, because they’re sure to have stories to share from their trip. As you become more comfortable with each other, then get into topics like hobbies and other interests. If you still feel like you’re getting green lights from them, you might even ask about family and make them a closer friend who you just happened to meet at work.
Return invitations. Emphasize the “give” in the “give and take” in any healthy relationship.
Perhaps most importantly, be the type of person you’d want to be friends with. This gets at the famous “golden rule” of treating others the way you’d want to be treated. Be the friend you want to see at work!