This seems like a no-brainer, but if you don't advertise your event, no one will come. It's really hard to show up to an event when you don't know its happening.
Make sure to take advantage of any in-game ways you can list your event. If you're in a guild, ask the guild master if you could hijack the message of the day. Send out an in-game mail to a few of your friends, and ask them to forward the invitations along. Take advantage of your game's official forums, but don't forget about fansites and unofficial forums! Not everyone comes to the official forums to read what's going on.
"If you find yourself stuck on coming up with a good event idea, it could be as simple as getting people to try that content they forgot about."
Finally, don't forget about networking. Don't invite your friends, invite their guilds too! If you're running an RP event, tap a few RP guild leaders on the shoulder and tell them what you're planning. They'll most likely be interested to hear what you have to say, and they might show up to your event with their guildmates. If you're running a PvP event, like a tournament, invite other PvP-centric guilds and form brackets.
Work with your game of choice: Look for interesting facets of the game
Nobody runs 4-man arena matches in Global Agenda, but it doesn't mean they're not fun. Players forget about Ballista in Final Fantasy XI, but that can be a good time too. Forgotten dungeons and PvP zones lie all over World of Warcraft -- maybe go exploring?
Look all over your game and take note of unused content, or forgotten areas. Just because that content is neglected doesn't mean it's not fun! If you find yourself stuck on coming up with a good event idea, it could be as simple as getting people to try that content they forgot about. Why not organize with a few Horde guilds and try to make a Silithus PvP night?
Also, try giving older content or features a new use. Why not create a puzzle mystery in EverQuest II with the help of a few well-placed books? Why not turn the towers of the Eastern Plaguelands into an RP event? Don't let the purpose of a piece of content get in the way of your imagination. That content may just work to your advantage!
Events are tough and chaotic, but are very rewarding and a lot of fun to boot. Plus, you might just meet some new people and make some new friends in the process! So don't sit there and let the game tell you what to do -- make some stuff up and have a blast in a new way!
Seraphina Brennan is the weekly writer of Anti-Aliased who has ran soooo maaaannnyyy eventttssssss. When she's not writing here for Massively, she's rambling on her personal blog, The Experience Curve. If you want to message her, send her an email at firstname.lastname@example.org. You can also follow her on Twitter through Massively, or through her personal feed, @sera_brennan.