The Great Ocean Walk was a fantastic experience and is one of the best experiences in our lives. Our tips would be toavoid the rock scramble in Wreck Beach unless you are particularly confident in your abilities but the wreckages on the beach are very nice. Practice as much as you can beforehand, especially for the uphill day.
Wear your boots several times before the walk. Any blister you get is one you won’t get during the walk. Also, good wool socks make a great difference.