Open up a bit. Don’t go full TMI, but make yourself a little bit vulnerable. Nobody becomes besties by only discussing the weather.
Close friends are what leads to personal discussions. But personal discussions are also what leads to close friends.
Via Click: The Magic of Instant Connections:
Allowing yourself to be vulnerable helps the other person to trust you, precisely because you are putting yourself at emotional, psychological, or physical risk. Other people tend to react by being more open and vulnerable themselves. The fact that both of you are letting down your guard helps to lay the groundwork for a faster, closer personal connection.
Close friends have a good “if-then profile” of each other. Once you have an idea of “if” someone was in situation X, “then” they would display behavior Y, that means you’re really starting to understand them. And this leads to good friendships:
People who had more knowledge of their friend’s if-then profile of triggers had better relationships. They had less conflict with the friend and less frustration with the relationship.