lol. Shall I, or shall I not help out a poor Baulko person... ooh! Wait! They called me a legend in their signature, so of course I shall!
(hghs rivalry instantly dissipates)
I would just sit down and write whatever. Normally, you'll get to about a page or two (or even half a page) before realising whether an idea is going to work or not. And for those of you who are writing lots of little "bits" that are often only a paragraph or two, calm down! My major work started out this way.
A writer who came to our school interviewed all of us individually after reading a sample of our major works. An objective view is an amazing motivator - it gives you another perspective to bounce off. Most of us 04's are nice enough to read your major works and critique if you were to ask nicely (we did our HSC - why the heck would we want to steal your ideas? lol). Otherwise, just go about writing.
For those who are stuck on plot, a good idea might be to order it in chronological order and then in gaps where you don't know what's happening, sketch in a few plot lines that could happen. Half the problem with stories is that you're not sure what to do with your characters or what sort of ideas to bring up. So write it out - plan your story. If you have something like "Jane needs to get out of the house and into the park", then you have a writing idea handed to you on a silver platter.
This is just one way of getting the ball rolling, of course. But where it doesn't work one way, always be open to trying it another way. Bashing your head against a brick wall only gives you a headache