People who enjoy playing with each other, can joke around and can consistently get things done together. You gotta have people willing to help each other out instead of oh well I already did this with all of my characters so no point helping you out. A good clan has to have a common ground that you should at least try and help fellow clanmates out whether it be nightfall/weekly, raids, exotic weapon bounties, leveling up low level characters, pvp, etc.