[found on fictionwriting.about.com]

“The most obvious way to pick a genre is to write what you like to read. If you mostly read romance, then write romance. Most of us read in several genres, and that can make it tricky though. Do you choose the one that seems the most marketable? The one you think is the most fun? Flip a coin?

This is ultimately a personal choice, but there are a few techniques that can help you choose:

• Make a pros and cons list. The classic decision-making tool. Write down the good and bad reasons to write in each genre and see how it shakes out.
• Go with your gut. After thinking about your options for a while, sit quietly for a while and listen to your intuition. Forget about marketing, or what your friends will think, what does your heart tell you to write?
• Pick the most marketable genre. This is tricky since it’s almost impossible to guess where the market is going. That said, you may be choosing between writing in a super-niche, micro-market, and something more mainstream. If you truly feel that they are equally-weighted in every other way, then maybe go with the one you think you can sell.

As you examine potential genres pay attention to the ones that attract you, but scare you at the same time. If you’re excited to write in a certain area, but afraid that you won’t be able to do it, then seriously consider choosing that genre. Often what you fear doing is what you need most to grow as an artist.”

[found on http://fictionwriting.about.com/od/genrefiction/a/How-To-Choose-A-Genre-For-Your-Novels.htm]