Basically, as long as you can justify essentially everything you do (ie, not putting it in there for no reason except to look good), your composition will score well. If you're looking at extended techniques, I would visit the Conservatorium library, and view scores by composers who made use of extended techniques. Composers like Berio and Stockhausen come to mind, though there are many more.
The next thing is to actually find players of the instruments, to demonstrate the techniques. It's no good writing a certain part if the instrument cannot successfully play it.
I would recommend a visit to a composition tutor - preferably one who is primarily a composer - before you complete your work. There are many composers throughout NSW who are more than happy to tutor you for a reasonable fee. If you're in the Greystanes area, I charge around $30 an hour, otherwise one of my colleagues may be more suited to your purposes.
