When making tour in Ethiopia, the forms of transport you use differ depending up on your choice of means of transport, the season & the road condition.
You may use flight both when you come into the country of destination (in our case Ethiopia) and while making tour in Ethiopia. The northern & eastern tourist circuit has standard airports. So it is possible to think of making your tour fully (or almost fully) by flight. But making a tour fully by flight is not possible for the southern route. But it is possible to make your southern tour somewhat a mix of both.
At present new trans-regional roads are being built and the old ones are being rehabilitated. Therefore, the Ethiopian road condition is much more improved except in some parts of the southern circuits which make four wheel land cruisers mandatory. But the North and the East are accessible both by buses and land cruisers. One of the main reasons that make the Ethiopian tourist destinations a bit expensive is this fact. Mini-buses are most often used for city tours and for destinations at short distances from the capital or major towns.
There is a rail road that extends from the central Ethiopia to the Eastern part of the country called Harar and which continues up to Djibouti. At present the trains are very old that, except the local people, tourists tend not to use them as means of transportation. But soon enough this might change because the government is taking some measures of improvement.
While visiting the islands on Lake Tana, or if you would like to cross in to the other region of the country on Lake Tana, boats are used. And also on other lakes & rivers of the country you may use boats for visiting, recreational, or rafting purposes.