That's a pretty pretty good question, I am sorry that I am invading filipino forums with english haha.
Well, I've researching about it for so long, and what things attracts players?
Emotions, when you feel excited about something it catches your attention, so a well made promo video is the best way, that + good advertising, and I think paying advertising on Facebook is a really really good idea, that + your video, you have a bomb.
You can also make a Pvp/WoE tournament before your server's opening, this will attract a lot of players, but also use facebook + promo video, and you have another bomb.
But what players look for a server is that is well managed and also the admin has to be profesional, and well skilled. Back in 2 years, when I was still playing RO, I remember that I saw a bunch of FluxRO servers, those where the Flux CP was their main page. Every1 of them, failed, because this will repeal most of the players, because that means that you cannot even make or pay to have a good website, so you might not be able to handle the server properly.
I hope I am not getting muted or something /sry