If you submit work to literary magazines, you will note that the guidelines almost always say something like, "To get an idea for what we like, read the magazine." And you read a few pieces and you think, "I can write as well as that," and you think that's the end of it. But, in fact, the editors are asking you to do some research. It's hard to know what questions they want you to explore, but here are some possible items to consider when you are trying to figure out what they like.
Genre. First make sure you know what your piece is. Science Fiction, Fantasy, Romance, Westerns, and Folk Tales are probably going to be accepted by different magazines than creative nonfiction or literary fiction. Poetry often has its own constraints.
Length. Is most of the work short or long? Does the magazine take work over or under a certain length?
Format. Do they handle unusual spacing or shaping of poetry? This is really hard in html, and your poem will not look good across all platforms, particularly mobile, if it has tabs. Print magazines may be able to accommodate format issues.
Subject. Have they taken work with a similar subject to what you are considering submitting? If so, they may not want a similar piece unless you have handled it from a different angle. Do they like subjects on the edge? From the heart? Conceptual? Ironic? Do you see violence? Judgment? Grief? Everyday problems such as divorce and death? Interior dilemmas such as guilt or shame? Moral choices? See this post for subjects to avoid, or at least to be careful of.
Tone. Does the work you see come from anger, love, curiosity, bewilderment? Is it written in a clinical manner or informally? Does it sound like it is trying to teach or show or preach? Authoritative or exploratory?
Language. Do they pay attention to the sound of words? Does every word seem to mean something? Do they like heaped-on images? Surreal and stream-of-consciousness? Matter-of-fact descriptions? Big words? Natural-sounding words? Creative metaphors? Simple similes? Clichés disguised as poetry (as in "the grass was a green carpet")?
Humor. I think the kind of humor appreciated by the magazine is the ultimate key. Is there any apparent or obvious humor? Some magazines are very serious. Some want broad comedy. Is the humor silly or clever, witty, sly, self-deprecating, or mean? The kind of humor is a clue. Does your humor match? Do you laugh at the work that is meant to seem funny? Your work might match, too. If you cringe, don't bother, this magazine is not for you.
Even after you go through this list, it may be hard to tell. But it is worth reading a large sample so you get some kind of intuitive feeling. You might even find some other writers you like. See how a magazine describes itself. Pank, for example, likes the gritty, experimental, sometimes shocking, Word Riot wants "forceful " "edgy" and "challenging." Generations is interested in "encouraging conversations across the generational gaps." Blackberry wants to "expose readers to the diversity of the black woman's experience and strengthen the black female voice." You've got to know what the magazine is about before you submit, or you are wasting your time and the editor's time. You can find a listing of magazines and their calls for submissions here.
Lastly, be aware that most magazines accept only 2-10% of the work they receive! It may be that you did your homework (You did! You did!), but your piece just doesn't fall into that acceptance category.
No matter what, good luck and keep writing!