hi i'm an italian 23 years old that is about to move in australia for improve my english and in the meantime to find a job.in the last 3 years i had work in engineering sector but i didn't finish last year of high school.i want to know which city,with hot weather,a good youthful presence and chance of utility man job,is the best.thanks in advance for your answer

I assume you're coming on a Working Holiday Visa are you?
And if so, you could find it difficult finding work in cities of say Sydney and Brisbane, warmest for Australia like European countries, the UK, China and USA etc. is feeling the global economy downturn and a lot of permanently employed Australians losing their employment will be looking for whatever work, casual or part-time is available.

I'd suggest that you have a look at www.wwoof.com.au - their bulletin board giving an example of work and you can register and get a guidebook on arrival or Help Exchange work for accommodation and food in Australia New Zealand Canada Europe not wwoof and though they are primarily for voluntary work, by getting food and accomodation in return at least it would help to lessen travelling costs.

There is also the possibility that whilst wwoofing in areas away from the cities you may through contact with the locals here about paid work and then there is also the seasonal work like fruit picking - Harvest Trail - Harvest jobs - Australian JobSearch

All such work could have you away from major cities but you would still meet younger people, perhaps travellers from other European countries amd if you find some work initially and save a bit then you can look at holidaying in other places.