I just received this link this morning and got on board straight away. I've got to say of all the campaigns on the subject, this one is great because it makes it really easy for you to do something and to stand up and be counted. Definitely worth a look:
http://www.whoonearthcares.com/
This was the customised bit I put into my letter, in the context that I sit in a safe ALP seat:
I am also concerned that the ALP is directing it's preferences to Family First instead of the Greens. I understand the practicalities of the preferencial voting system and why the ALP may consider this necessary, but it sends a very odd signal to send preferences to a party which normally would be diametrically opposed to the ALP's traditional values. I would have through that the Greens were more ideologically aligned with the ALP's core values.