Dar Es Salaam and Arusha with their international airports are the best places to start your tour in Tanzania. You can choose if you want to travel from Dar Es Salaam to Serengeti or the other direction from Serengeti to Dar Es Salaam.
Dar Es Salaam is Tanzania's largest city and known for its horrible traffic jams. So if you would like to visit the city centre (e.g. to visit a museum or the fish market or go to the ferry terminal), you should plan enough time for transportation.
Nice places to stay overnight are a bit outside the center along the beach.
From Dar Es Salaam you can take the ferry to Zanzibar, which takes about 2 hours. You will arrive in Zanzibar Town where you can visit the old Stown Town.
The beaches of Zanzibar are perfect for diving and snorkeling.
About halfway on the road from Dar Es Salaam to Arusha you will pass the Usambara Mountains. The mountain range is covered with tropical rainforest and lots of vegetables are grown on the hillsides. The area is ideal for hiking and there are stunning viewpoints.
The town of Lushoto is easily accessible from the main road and offers a few places for accommodation.
Arusha is the place to start your safari to Ngorongoro and Serengeti. So it is probably best to spend one night there.
Ngorongoro Conservation area is named after Ngorongoro Crater, the largest unflooded and unbroken volcanic caldera in the world. You can enjoy wonderful views from above and when getting down into the Crater. The area contains over 25,000 large animals including black rhino, hippo, buffalo, wildebeest, zebra, eland, cheetah and lion. The legendary annual wildebeest and zebra migration also passes through Ngorongoro.
The famous Serengeti National Park hosts the largest terrestrial mammal migration in the world. It is also renowned for its large lion population. Approximately 70 large mammal and 500 bird species are found there.
It is the perfect highlight to end (or start) your trip in Tanzania.