Due to previous low water supplies Melbourne is big on saving water. Water restrictions are currently in Stage 1 (click the link to see what this means) so you don't have to be too careful, but you'll find most locals are pretty water saving savvy. Having shorter showers and not leaving taps on unnecessarily would be a common courtesy.
Melbourne's blue skies can quickly turn cloudy - then rainy, then stormy, then hail the size of golf balls - so be prepared and carry an umbrella and a warm jacket from Autumn to Spring. For further information please refer to Crowded House's song 'Four Seasons In One Day'. Totally relevant.