Winter is the traditional time for planting deciduous fruit trees, though this can easily continue through Spring as long as the trees are well watered through Summer. 

Spring is the perfect time to plant frost-tender fruit trees like citrus, passionfruit, tamarillos and avocados.  Winter planting can be tough on these sensitive plants, being too cold for the soft young foliage as well as often being cold and wet for the roots.  Once the risk of hard frosts has passed, plant these trees in your garden (or in containers for small sites).  If forecast overnight temperatures drop below zero, throw some frost cloth over the tree.  Liquid Frost Cloth (aka Vaporguard) is a pine-resin-based substance which can be sprayed onto the leaves as frost protection (it coats the leaves to prevent the water inside the cells of the leaves from freezing). 

Avocado trees have very sensitive roots so should be treated carefully when planting. Often nurseries won't supply avocado trees until November when the soil temperature is increasing and isn't usually too wet. Never carry a young avocado tree by the trunk, always pick it up from the bag.  Carefully remove the tree from the planter bag, by cutting the bag off (don't yank it out by the trunk!).  Disturb the roots as little as possible.  Plant into free draining soil. Check the soil's drainage by digging the hole, filling with water (or wait for a day of rain) and see if the water drains away. If it hasn't drained after a couple of hours, choose another spot.