To make it short:
-Stand out. You're up against a sea of practically identical servers. Do something on yours to make it not the exact same. No, factions + crackshot or some other individual plugin isn't a big deal.
-Polish. Don't use crappy grammar, proof your posts, make them look interesting. Bad ads don't do well. If you show effort (not just in the ads) you've got something.
-Be active. Extremely. Owners that aren't active kinda tell players that the server isn't worth spending time on.
-You can do the looking for staff grab. I personally detest the practice, and it makes me even less likely to join, but some find it effective.
-Make the server yours, goes with polish. Customize the configs. Your own join messages, leave messages, custom death messages are fun twists... stuff to give your server a point to existing. Just factions + a couple other plugins on default settings doesn't give a reason why your server should be any better than others.
-Don't expect for any of this to work. You can have the best executed server and still fall flat on your face - ownership means fighting massive over saturation, largely by people who only open servers to say they are owners without contributing to the minecraft community.
-Don't make idiots staff. Put in staff that have brain cells. Think this is a "no duh" thing to say? You'd be surprised.