1. Spend a Sunday with them. Not a Saturday night, when everything is bustling and loud and socially seamless. Spend a Sunday morning with them, tired and hungover and without plans for the day. Eat breakfast together and don't fix your hair. Experience each other without needing to entertain.
2. Be comfortably silent. Go for a long drive and allow for bouts of quietness as they naturally happen. Existing in someone's silence is existing in the most intimate part of their life.
3. Call them when you're not OK. Take them up on the promise to be there for you no matter what. Tell them the truth. Let them comfort and console you. Tell them that you're there for them if they ever need it. Hold true to that promise.
4. Hold space for them. Listen to what they have to say wholly. Without anticipating your response, without checking your phone, without wandering eyes. Give them the entirety of your energy. There is nothing more precious and sacred and rare.
5. Talk about ideas. What you believe in. What you theorize about existence, or what fate could have in store for you in the next five years. Just move beyond discussing people and events and petty, daily grievances.
6. Read each other's favorite books. Trade your personal copies -- the ones that are highlighted and marked up, where the binding is almost completely breaking loose from having been flipped through so many times. Share with them something that opened your heart and fed your mind.
7. Create something together. Start a little business or work on a story or paint pictures for fun. Go on a service trip or build a coffee table or redecorate your respective kitchens. Do something where you team up for a greater cause.
8. Pay attention to the little things. Notice what they're often most bothered by, what their favorite flavor of ice cream is. Know their Taco Bell order so you can surprise them with it. Not everybody is naturally detail-oriented, so make it an intention to be. People appreciate it more than you realize.
9. Attend your respective religious/spiritual services/practices together. For the sake of understanding, go to their church service one Sunday, or show them how you meditate, or ask them what they believe and why. Let them be your guide through something you otherwise wouldn't know. There is something absolutely extraordinary in learning about someone else's culture or dogma or lifestyle -- in practicing what it means to lovingly coexist.
10. Plan a short trip. It doesn't have to be elaborate or expensive. Explore a neighboring city for a day or go for a hike. Plan in advance so you have something to look forward to.
11. Integrate them in your other social circles. Merge your friends together for a wine night, no matter how deeply you're convinced they'll have nothing in common. There's something so intimate and special about gathering all the separate parts of your life in one place.
12. Always show up. To their baby showers and art shows and graduations and moving days. Not because that's "what good friends/boyfriends/girlfriends do," but because that's what you do when you care about someone else's happiness as much as you do your own.
13. Plan your heart-to-hearts. The older you get, the more inconvenient it becomes to talk until 3 a.m. (there's work to do and groceries to buy and parents to call and you get the picture). So plan ahead, if you must. Decide to have a sleepover and keep the next day open so you can stay up and sleep in and relive your middle school glory days.
14. Talk about your families, and what it was like growing up. It's one thing to meet your friend/boyfriend/girlfriend's relatives, but it's quite another to hear the whole story, the reality, the not-ready-for-company, imperfect picture of what they experienced. This isn't a call to needlessly air the dirty laundry, but rather an articulation of the fact that you won't really know somebody unless you understand the truth of their foundation.
15. Be unfiltered. Don't mince your words or tailor your opinions or only present the side of you that you feel is "acceptable." If they don't want the whole of you, the truth of who you are, then they're not right for you anyway. And more importantly, people can sense genuineness, and will subconsciously take it as a cue that they're free to be who they really are as well.