If you spend a lot of time visiting writers' forums, you may encounter differences of opinion on whether to "write to a market." For those who may not know, writing to a market essentially means letting the market you wish to sell to dictate how the story you write will work. This can happen either before or after you have actually drafted the story: some writers will read quite a bit of material from a particular market to get a sense of what those editors might like, and then attempt to craft a story that fits those parameters; others will have an idea, sketch it out, then pick a target market and (again on the basis of reading what has sold to that market) tune the story to fit. The fit can be stylistic, content-based, or even one of length.
The argument for writing to a market goes something like this: "Of course you should be aware of what a particular editor likes before you send something to him or her. If you don't keep those editorial tastes in mind as you write, your chances of a rejection will go way up."
The argument against writing to a market goes something like this: "Of course you should be aware of what a particular editor likes before you send something to him or her. But chances are you'll be less true to your story, or lose touch with your Muse, if you try to cater to editorial tastes too directly. Your chances of a rejection will go way up."
Both of these agree on two points: 1. It's good to be aware of what an editor likes, and 2. Your chances of a rejection are quite high.
I confess I have difficulty writing to any particular market. When a story idea jumps into my head, I have to write it the way I have to write it. Some story ideas demand a higher word count for me, and others a lower. Some story ideas call for more description, and some for less. Some call for lush voices, and some for spare ones.
You could say that I write to a market now, because I do design stories specifically for Analog magazine. On the other hand, the fact that I wrote a story that Analog wanted to buy was pure coincidence. It was a story that asked to be told, and I had a great tip from Sheila Finch on where to send it. It was only after that that I decided I should deliberately look around for stories to tell about language and culture for the purposes of sending them to Analog. Fortunately for me, I find that alien design, and language and culture stories are incredibly inspiring. The fit is natural.
If you are not going to plan to write to a market, then finding a place to get your story sold will be a little like the process of finding an advisor for a Ph.D. At that point in your studies it's no longer a question of whether you're a good enough student (feel free to substitute "writer"), it's a question of whether there's someone out there who wants to work with you. It is a question of fit between what you can do and what the writer or editor wants.
I can't say I don't envy those around me who talk about writing to specific markets, particularly when they appear to be able to do it successfully. I suppose one could look at submission guidelines for clues, or read a lot of material from the magazine, or find editor interviews online. After that, though, a lot of guessing is involved until you actually manage to make a sale.
Be careful that you don't lose your convictions in your efforts to do what an editor appears to want. Many editors have idiosyncratic, eclectic tastes - you never know what may appeal to them. It could be that if your story resembles some they've seen before, that they'll love it - or it could be that it will strike them as derivative.
I believe that there is wiggle room. If you have a great story with a dynamite core conflict, and you manage to keep its drive going all the way through, then you can play around with thematic and textural elements to give it a somewhat different flavor.
I have a friend, though, who told me something quite fascinating about a discussion he took part in about international science fiction. Several of the people involved came to the conclusion that international sf was often more exciting precisely because people weren't writing to a market, and thus were pushing their ideas further than they might otherwise.
I encourage people to look for highly original ideas, no matter how they execute them. Originality can be tricky, but one thing I've found useful is looking around in my personal experience for story ideas rather than looking for them in stories I've read. Of course, taking traditional story tropes and turning them on their heads is another favorite hobby of mine.
In the end, I think it's important to write what inspires and excites you. Because if you can't get excited about a story, it's hard to imagine how anyone else will. Yes, I do rather believe in the Muse, though I think she's less intractable and more cooperative than many others do.
I wish all of you the best in selling your work, wherever it happens to land. Because I love reading good stories.