If you're anything like me, what you'll scribble on a scrap of paper and toss into your "story ideas" file will most often be just the core of an idea… something that struck you as a possibility for a piece, but not something you've really thought through. 

So when you sit down to decide on the actual story you'd like to write, you must make sure that your idea is -- 

Specific

Don't send a letter to a publication asking if the editor is interested in a piece about Belize. Instead, ask if he'd be interested in an article about the best jungle lodge or the top spots to invest in real estate.

Unique

If you've been reading a lot of travel stories, you'll develop a sense after a few months for what's run-of-the-mill and what's new. Also, by keeping country files you'll have on hand some examples of what other people have written about the place you're going to write about, so you'll know in what ways your piece will need to be different. 

I've found that one way to keep ideas unique is to think about what the stereotypical view of a place is and write to counter it. If most people know about the diving in the Bahamas, then you write about the hiking trails. 

Targeted to a particular audience

When you target a particular audience with your story idea, it becomes a stronger idea. Here's what I mean: If I were to write to the readers of Walking magazine about St. John in the U.S. Virgin Islands, my story would, most likely, be about the trails there -- the best walks, the best guide, the best time of year to go, maybe the best "outdoors" hotels to stay in. 

That story is specific and it's unique -- at least to the readers of Walking magazine. While you might regularly find stories about St. John in travel publications, it's not run-of-the-mill fare for Walking.