I've never finished short fiction to try to sell it, but a lot of what I've seen from different sites and magazine submission guidelines is to know the market you're selling to, and to know the kind of target audience that reads the magazine, and the type of work the magazine generally publishes. A suggestion from I think Realms of Fantasy was to buy a couple issues of a magazine you're considering submitting to, and read what they put out. So that you don't do something like submit a blood and guts horror story to Asimov, or something like that. There's also a website I found, though I have no clue what it was now, that gave a lot of option to search for and came up with a list of places, along with how they accept submissions, payment, and sometimes a link to guidelines. I might possibly have the link somewhere on my home computer.
