i) A clear set things which are known to be off-topic. (Topics which are almost entirely polarising, where you're never going to change someone's opinion, and normally not welcome here.)

ii) Insisting on reasonable behaviour, letting users know what's expected, and being able to down mod them when they fail.

iii) Use of down arrows only to moderate unsuitable comments, not just comments with which you disagree.

iv) A niche target audience, who may need to buy / sell things to from each other, or who may work for each other, or who may need to raise money etc etc.

If you're interested in online communities I usually recommend "meatball wiki", but that's more about wikis.