As someone who has made a thread with 0 replies and a thread with 1,500 replies I have figured out that it mostly has to do with the title, it has to be interesting, attractive, weird, or any combination of those to attract people in. This is why threads like "Ban the Member Above you for no Reason" are so popular, it's because when you see that title you think "Ha, that's a fun idea, and I really want to have some fun and ban other members!".
Another thing that works is when you have a thread that doesn't require any real effort or thought. Take my "Describe the member above you in 3 words" thread, you look at the title of that and think "Good, all I have to do is get in, look at someones name, and type three words". That very simple thread has gotten 1,500 replies for no other reason then the fact that it is kind of fun and extremely convenient.