I just send it out with no real expectations. And I don't write TO markets nor do I even try to match the market. I write whatever story pops into my head and if it's a fantasy, I send it to all the magazines Duotrope says accept fantasies. Likewise other genres.
You're probably in the majority, but my experience says you won't sell many stories this way, unless you've actually read most of the magazines on your submission list.
When you actually read a bunch of magazines, you do write to the market, consciously or not. The stories that pop into your head will be based on stories you've read, at least in style, tone, mood, etc.
There is a good bit of commonality in the markets, which means a story written specifically for one magazine in a given genre may sell to a different magazine in that same genre, but this generally only works when teh writer actually reads a pretty fair number of different magazines.
When reading the slush, an editor can usually tell immediately whether the writer actually reads the magazine, and it's just real tough to sell many stories in any genre unless you spend a lot of time reading the various magazines.
One thing that hasn't been mentioned here is a trick I learned a long time ago, and that's writing a story aimed at a particular magazine, but a story of a type that magazine has never published. I've made some of my best sales by writing a children's humor piece for a serious adult magazine, or a story with serious adult overtones to a children's magazine, or a genre piece for a literary glossy, or a literary piece for a straight genre mag.
Sometimes reading outside your genre can give you new markets, and give editors stories they simply don't get from anyone else.
