The first step is to think about what you read. What's most similar to what you write, and what are their submission guidelines? If it's a magazine, you may need to request submission guidelines, but most book publishers will have guidelines somewhere on their website.
Obvious places are the women's magazines. The UK and Australia have pretty good market (I don't know about the US), though a lot are limiting their submissions to their current writers at the moment due to the sheer volume of submissions.
Womag Writer's blog collects submission info and other news about the mags. If you can, try and get hold of a copy first; there are small but significant distinctions between what Take a Break and People's Friend want, for example.
Some romance publishers do anthologies from time to time. The best way to find those is to keep a close eye on their submission pages or follow editors' blogs. Also, stalk the BR&BC forum here; a lot of people discuss the current anthology calls and sometimes even the editors pop in to clarify what they want.