I came back from travelling Australia and NZ in June this year. I went for a year and it was great!
Definitely try and go sooner rather than later as some visas are restricted to age. For example Oz and NZ you can only get working holiday visas up to the age of 30.
I worked in offices while in Oz but many of the friends I met and made while out there did fruit picking or cattle/farm work. This can actually extend your visa too if you do this type of work. A normal working holiday visa lasts a year.
You'll have an awesome time and meet loads of people and make new friends, I thoroughly recommend going travelling :-)
The websites I used to help me plan my trip were:
http://www.gapyear.com
http://www.lonelyplanet.com
Both of these are full of some great tips and advice from people who have been there, done that, got the T-shirt!
I ended up booking my trip through:
http://www.realgap.com
Just to put my mum's mind at ease but you can easily do it yourself. :-)
Wherever you end up going you will enjoy yourself and have fun!
Good luck!