try to make the server well known, post it in every possible site/forum (without ofc spamming it) and add some preview images (from your zones/npcs,custom items etc.) way before opening (like 2weeks or more)
create a forum for the srvr and inform playas about updates/changelogs,add sections for clans to join,create a community wich will discuss daily on server issues,updates or cpclan recruitments.
Ask playas or friendz for help,testing the whole gameplay in detail (like every buff stat,or skills working etc.)
Do beta tests so playas who try it can have a smell of how it looks like,and fix issues at same time,do events(even pre-opening,) and reward with usefull -but no op- items
try premium advert on topsites,create a promo vid and share it and find a good opening date and time,in general try be more creative with every step u making,some small changes here and there..and imo,don't over do it with them custom items.. anyways,still noone says that it will succeed but you have for sure try harder than just advertising it half day before opener...