It's extremely easy to find out what topics are in demand by doing a little Internet surfing. In fact, the Internet is actually the best place to research hot topics. It's far better than the library, chain bookstores, print media, or television. Today's publishing trends will appear online first, long before they hit the bookstores.

Before you write anything, try to think like a publisher. Ask yourself, what do they want to buy?

Above all else, publishers want to print what is going to sell. For example, if you want to submit a book proposal to a publisher, go to the Web and find out what the hot topics are in your chosen field. As a writer, you are, by nature, a researcher. The Internet is a researcher's dream come true.

For example, if you are a computer nerd and want to write about technology topics, what is the latest "buzz" on the propeller-head discussion boards? What are people complaining about? What new techie toy is your average 14 year old dying to get his hands on?

Or let's say you want to break into a magazine. Every single magazine editor on the planet, without exception, will tell you to "read the magazine first" before you get in touch.
Many, many magazines put their writer's guidelines online. If they don't, you can usually read a few issues online to get a feel for the magazine's tone. You no longer have to waste postage begging for a copy of the magazine before you contact the editor or publisher. All you need to do is get online, go to your favorite search engine, and start digging.

If you're interested in a particular magazine or trade journal, simply to go your favorite search engine such as Google. Then type:

[the magazine name] +guidelines OR
[the magazine name] +"writer information"

For more general searches, try these phrases:
"editorial calendar"
"writer's guidelines"
"author's guidelines"
"contributor's guidelines"
"write for us"
"freelance writing markets"
"freelance markets"
"writing markets"

Yes, the quotation marks are important. They tell the search engine to find the entire phrase, as opposed to the individual words. You also might try derivatives of these searches, such as "writer guidelines" and "writers guidelines". Sometimes web sites or search engines aren't good at handling punctuation, such as apostrophes.

Armed with a little information, you can give publishers what they want. And in turn, they'll give you what you want: a byline!