From almost all of the... by Dirim
From almost all of the capitals of Europe, you can find flights to Ankara. The airport is quite far from city center, so do not try taxi. The shuttles are reasonable.
From other cities to Ankara you can come by Train, or Bus. Buses are faster and more comfortable but be aware of the high percentage of traffic accidents.
Istanbul is 6 hours by bus, 7-9 hours by train (rare)
Izmir is 9 hours by bus, 16 hours by train.
(Trains are ceheaper in Turkey)
Try Dolmus, although they are not good in Istanbul, in Ankara Dolmus is the best and fastest way to travel, but, of course select metro or Ankaray if it reaches to the destination you want to go.
(Photo: Road from Gölbasi to Ankara...an old one. Contemporary Ankara is surrounded by motorways)