You can make a thread about it here on the forums - give some detail about your arc including targeted levels, foes, general story teaser, etc. Make sure to listen to any feedback and consider making changes if it's good feedback. You can enter it when some people call for arcs for contests, such as here:
http://boards.cityofheroes.com/showthread.php?t=248915
Make a point to participate in whatever discussions you have something to add to here on the MA forums; having something about your arcs in your sig helps. It also helps to participate in other AE-related things such as this:
http://boards.cityofheroes.com/showthread.php?t=265388
Another thing you can do is start a thread offering to trade plays and reviews with other players.
Yeah, it ain't easy. 
About the one thing I've found that works consistently is to get out there and push that arc or those arcs of yours hard. Most of the plays I've gotten in the past have been a direct result of my pushing my arcs and personally joining/leading the teams in question (though I usually ask someone else on the team to host so they'll get the full experience of seeing clues and text). It seems to work, but it means I've basically felt like I was fighting for each little rating, usually one, two, or three ratings at a time if I get lucky.
It's frustrating, yes, but it works.
Also, getting involved with the MA Arc Finder chat channel tab in the game and getting to know folks in there, offering up play-swaps with folks, seems to help, too. Clave there has given some good suggestions, as well. 
I'm out of signature space! Arcs by Tubbius of Justice are HERE: http://boards.cityofheroes.com/showthread.php?t=218177
In addition to the above:
1) Submit your arc & description to cohmissionreveiw.com and masearch.somee.com
2) Seed your arc description with relevant Keywords (most AE players looking for STORY will search by Keyword)
3) Post your arc on your server's MA Arc Announcement thread
4) Whenever you leave comments on someone's arc, ask them to repay the favor and play/rate yours
Good luck, and have fun with it!
Craft your inventions in AE!!
Play "Crafter's Cafe" - Arc #487283. A 1 mission, NON-COMBAT AE arc with workable invention tables!
Push push push, if you really wanna get your work out there and shared. Just letting it sit won't get results. Be active here, pimp it's best features, and so on. Having some kind of selling point, or hook, is a big help. You've gotta be able to answer the question of: What makes joe-hero or jane-villain want to stop when they see your ad, and think "I had better try that out!"?
For an example, my lone arc has been sitting in my signature since the launch of architect, and while I've refined it somewhat over time, it's basically been there in the system since day 1.
And it has 18 rated plays. And if the rumblings of frustrated authors are any indicator, I've done fairly WELL for not really advertising at all. And I have put almost zero effort into advertising it, mostly because its a fairly mediocre "Go beat up these bad guys" arc that doesn't really have much to write home about. Mostly I made it for myself, so I'm content with that, but if you're interested in sharing and being seen, it's gonna take some effort.
Mission Arc: Metatronic Mayhem (Id 1750): A tale of robots gone wrong, rogue robots gone right, and madmen gone every which way but loose.
Oh, duh. You could also submit your arc to the AE Storyteam for play.
Just be sure it's in a final or near-final state and you've play-tested it yourself, first.
Craft your inventions in AE!!
Play "Crafter's Cafe" - Arc #487283. A 1 mission, NON-COMBAT AE arc with workable invention tables!
I want to mess around with Architect, but other than some stuff for me and a few friends, it seems pointless. Anything I do will be buried under farms or wind up back on page 30.
I know my stuff's not great. I haven't done this long. I don't even have anything published right now, I just make something, mess around then unpublish since there are so few slots while I figure this out. But when I do decide I want something out there, how will I actually get it played? Having it ignored would just be discouraging.