Magnemite coil is a way to increase your join avenue. What you do is catch two magnemite. Put on up for trade and ask for a magnemite of any level in return. Once that magnemite is up for trade, search for another magnemite any level that someone wants to trade. Trade your second magnemite to the person that wants a magnemite of any level in return. Rinse and repeat and your join avenue will increase pretty quickly.
Honestly, the best way to do it these days is to put up a Magnemite yourself, walk away for a bit, and come back later; your offer will more likely than not be accepted within an hour or two, if not faster.
Honestly, the GTS would be LOADS better if it treated those "already traded" options logically; just pull them from the queue. There's no reason at all to pull up completed trades when I want incomplete ones -_-
Even though I was one of the people who first helped publicize the Magnemite Coil here, I've definitely realized that the Dream World is a better way to get Join Avenue visitors at this point. Since the Coil has slowed down quite a bit since the game's release, it's better used as a supplement to the Dream World method rather than a replacement.
Also, look up "dw.exe" if you get the chance. It lets you get a lot more Pokemon/Items out of the Dream World in a lot less time, which frees up more time to go to other people's dream houses and gather visitors for the avenue.
They took for granted your soul, and it's ours now to steal! http://i.imgur.com/SkZftXF.jpg
A much faster way to grind out JA visitors is with GTS negotiations. You can easily pick up 10 or so visitors in an hour.
Just select Trade With Anybody, and as soon as the trade starts cancel out. Usuasally takes less than 2 minutes for the entire process. I got my JA from just opened to lvl 15 in a week like this only doing it an hour a day.
Just remeber to visit your JA and clear out your fans before you start so that you can get the max number of visitors per trip.