It is difficult to know about job prospects as it is very dependent on what subjects you can / are prepared to teach. However, secondary school teacher is on the list of occupations in demand and this is an area of rapid population growth with new schools opening.
I had no difficulty in finding work although my subject is Physics. It is very easy to apply to the state system (it is all done online) and I was able to start this before leaving the UK. I arrived in Perth in August and on arrival was invited to interview for the first job I had applied for. I was successful at interview although the job did not start until the end of January. I then applied to a relief teacher agency and was offered work the very next day. I also applied to the state government's pool of relief teachers which quickly resulted in a short-term contract up which lasted up until my main job started. All good!
Work in a secondary school in WA is very similar to working in the UK. As you would expect there is a variety of schools. Pay and conditions are superior to that in the UK in my opinion. The salary after nine years experience is around $98,000 and UK experience is taken into consideration for the salary scale. It is much easier to take leave during term time (albeit unpaid). You receive 10 weeks paid long service leave after 10 years of service and then every 7 years thereafter. And most importantly no Ofsted. There are no GCSE exams and all external exams are taken at the end of year 12 and are a similar standard to A-level. Students must stay in education to complete year 12.
My experience is in the state sector so that is all i can comment on. However there is a thriving private school system that should not be ruled out when seeking work.