Keep board list small unless a community grows enough to warrant their own.
Holding fun events, raids used to be the thing, but in modern times I think most anons are too afraid of getting v& (and with the current trend of law enforcement, I don't blame them), but cytube as >>105
suggested, (changing) word filters imo are fun forced memes and culture if you don't go absolutely nuts, game servers like minecraft, terraria, killing floor, etc. an ever changing board such as /777/ on 7chan can also be something to look forward to.
Accepting the fact that alt chans are almost always confined to small population and that isn't necessarily a bad thing. Imageboards aren't that popular anymore, any steam they had for forming huge communities has been stolen by reddit, discord, facebook, and co. The only reason a lot of kids posted on 4chan and 8ch was because of le anonymoose haxor anime meme king reputation, most people don't seem to be really interested in group psuedonymity instead prefering a platform with names and reputation.
Also change the fucking rules from "No doxxing" to "No doxing"