I work in development as the day job, so I have a bit of experience in story and in structure. Some might not agree with my advice, but you can take this however you want. If you want to go more in depth and ask tons more questions, I'm always open to emails (zac at scriptchat dot com) as long as you put HSX in the subject line, I won't overlook it.
First, you need to learn how to tell a story and the king of the mythic structure that you should digest is the works of Joseph Campbell. Since he's taught in some high schools and colleges, you might be able to find some of his books at your local library. I would recommend The Hero with a Thousand Faces and if you can find it, his video series on the Hero's Journey. You'll see most great stories (along with even crappy ones) tend to follow this paradigm. Also, Dan Harmon has a circle that he uses in his writing that you can find online if you search for his methodology that is Campbell simplified.
As for screenwriting books, check out Save the Cat as it is one of the best on structuring your plot. He's one of the "how-to" writers that actually sold scripts and was produced unlike most out there.
You can also join us on Twitter every Sunday night at 5 p.m. PST with the hashtag #scriptchat or visit scriptchat.com for past transcripts and we talk a different subject every week or have different guests that will tackle a topic and/or answer questions. I know it's early Monday morning for you, but we have a couple Aussies that drop by every now and then.
I would also try to read as many scripts as possible and dissect them with what works and doesn't work. Only read scripts in the PDF format so the formatting and pagnation is right. I've learned more from reading scripts than I have from any how-to book, including Save the Cat and it has helped me in my own writing endeavors.
And don't be afraid to just write. I'm the type of writer that will type out a vomit draft (after making an outline to know where I'm going - but can diverge from) in the matter of weeks. The true art is within the rewriting and really getting to know your characters, their stories, and where the script is going with the message you want to say.
I don't have much work online, other than the webseries I co-wrote called Wave Goodbye. We shot a 20 part webseries that equaled a feature film in length. There's some stuff I'm really proud of in there, along with some stuff that I wish was better. But to do it at the budget ($5.5k USD) and the limitations, it shows you can still do quality work. We raised our money on IndieGoGo, including a fellow Aussie that threw up a good portion of the money.
I'm finally to the point in my writing career where I'm happy with what I'm writing. I have a mix of different comedy genres (Hard-R, family, high concept) that I feel are commercial and would be worth the investment. Of course these aren't the first scripts I've written, as those are tucked away in a drawer to maybe be rewritten some day. As with any artform, you grow in the craft with each new project and time spent on the passion. My goal for 2012 is to finally find a home for one or more project, to possibly land representation if don't use my own contacts, and to write a feature versionof the webseries.
As for shooting your own stuff, I would reccomend starting with shorts first to get your feet wet. I've only directed one short before, and I soon realized that isn't what I wanted to do. I'm more of a creative person with the words on paper and I like the producing side, but I don't care about directing one bit. Some people are best to have others direct their projects as they become too close, and I think some people shouldn't be multi-hyphenates as you'd get better results with other opinions or visions helping bring it to light.
Okay, this has gotten a little long, so if you have any more questions... shoot me an email or ask here. I'm always here to help pay it forward. Why do I do it? Because over 95% of the scripts read are utter crap. I've spent countles hours reading (and passing) on projects for one reason or another, so if I can help some people grow their craft it is worthwhile and means less time spent on horrible scripts.
Good luck on the journey. After writing 10 feature scripts I think I finally have a handle on it. For some it might come earlier, but most will take years of struggling. The stories you hear of an "over night success" are not the norm, and most of those have been working at it for years.
My biggest accomplishment is finding a writer when he was 16. He had a great voice and really knew dialogue, but his problem was in story structure and finding a commercial story to tell. Five years later, we finally have a draft we're all proud of and is into a major agency for packaging. In those years he's grown as writer, produced some of his own little shorts and web content, and is now ready for the big time. With patient and practice, along with a huge stroke of luck, the doors of Hollywood won't always remain closed.