You are in the west of Devon and not far from the Cornish border. Roads are slow going in that area. Obviously you should see Dartmoor which is just a short distance to the east.
I would take a full day trip down to the area called The South Hams. Aim for Salcombe but try & park on the edge as it is full of narrow little streets with people. Then try and use the coast road via Torcross (see memorial to those who died during the war) as sit Dartmouth. Totnes is also worth a look in this area.
Going SW from Tavistock into Cornwall, aim for Looe and then try and go around to Polperro.
Going NW from Tavistock - visit Boscastle & Tintagel on the Atlantic coast. Clovelly is also worth seeing on the north coast.
Google the places mentioned and find them on Google Maps and check out the street view.