By sharing experiences.
Not just by talking about it, but sharing them like experiencing them together. I've looked back upon some uncommon friendships I've made that are now stronger than relationships by people I've just met at college or work.
1. We went out and experienced stuff together. Makes us closer and gives us memories to reminisce upon.
2. We've had points of mutual interest and that kind of gave us a push to be together more often and experience more. From music, to programming, to specific food.
3. We made mutual connections. I plan something with friends, I invite them, they invite theirs sometimes, such stuff.
4. We shared stuff about each other. Dreams, goals, relationship talk, stuff like that.