^Ohoh, Kirito. :'D
Anyways, for the newer/to air series I choose my anime (and series in general) based on their short summary on the season preview list. That in combination with the promotion picture put next to it might already give me an idea if it's something for me. I say that, because the artstyle is a major factor to me when it comes to watching/reading something. I don't care how good a series is, if the artstyle is not to my liking chances are high I won't watch it.
Usually I don't find that many series in the episode preview, but this fall season that was quite different. I stumbled on a site that had the trailers. So, that counts as well.
(K, Tonari no Kaibutsu-kun)
For the older anime, I rely mostly on recommendations from other people. It's how I found D.Gray-man and Fullmetal Alchemist.
Sometimes the opening song might play a role as well (Saiunkoku Monogatari, Hiiro no Kakera) or pictures, reviews that can be found on the internet. Sometimes I check out the "if you liked X you might also like ..." on MAL. : > It's worth a try now and then.