Many people, especially overseas visitors, expect to be able to see all of Tasmania by making perhaps just two or three day trips out of Hobart. Such will never do justice to this beautiful island. You really do need to drive right around - this eight-day recommended itinerary is probably an absolute minimum. Indeed, if you have an extra day, you could include a night at the West Coast town of Strahan. And if you have more time you could venture inland to Campbelltown and Ross, though the visit to Richmond will give you a taste of historic townships, bridges and churches.
If you live anywhere in NSW, Victoria or South Australia it is an easy drive to Melbourne from where it takes nine hours on the Spirit of Tasmania to get yourselves and your vehicle to Devonport on the Tasmanian North Coast. I suggest you book your passage and accommodation at least three months in advance, especially if you include Strahan. Alternatively, you could fly to Launceston or Hobart, hire a vehicle and begin your trip from the corresponding day in this itinerary.