I'm good at making acquaintances, but not so good at developing deeper friendships. Thankfully, my husband is great at this and if I follow along, we make awesome couple friendships that I deeply treasure. As I grew older, I have been comfortable settling with the notion of a very few really close friends. The #1 thing I have found works is like many other posters say - to BE a friend. And yes, it takes effort on my part - shoot a text semi-regularly, invite them out for such and such, have them over for dinner, etc. The friend I am closest to now....we weren't that close for many years. When she went through a separation, I was there for her. Checking in regularly, dragging her out to do fun things, accepting when she would flake on me because some days getting out of bed was too hard, etc etc. We grew very close during the couple of years after her separation. She is an amazing person and I gained a wonderful friend.
When I was looking for friends, I would invite acquaintances I found interesting over for dinner. At one point, my husband and I committed to inviting someone over for dinner once a week. It was a lot of fun and really good for developing friendships. I was rather surprised at how receptive people were to dinner invites (although we did deal with several flakey no-shows). We always held our breath if the phone rang on the day of the dinner - since it would often be a last-minute cancellation. Regardless, we had a lot of fun doing it and enjoyed all the excuses to experiment with new dishes.
There's a few people I know that I would love to get to know better...sheer laziness on my part has really limited me. I should invite them for dinner or out to some event or whatever. Definitely something to consider in the New Year.
I do find building friendships to be an active thing on my part. Sometimes a close friend would fall into my lap....but most of the time, it takes active engagement from me to make the effort to invite them out to do something we mutually like, etc etc.
@swick The folks we have gotten along the best with all like board games although Mexican Train Dominoes is our game of choice :) While I didn't consciously choose friends this way, it does make a rather awesome filter!