Ravenna is not located on a main line of Italy 's train network. Coming from Venice in the north, or from the south you'll probably have to change trains and endure a long day of travelling with limited time in Ravenna if you plan to visit the city in one day without staying overnight.
Travelling by car to Ravenna is the most practical if you are touring Italy by car and plan to visit Ravenna as you travel between other major ports of call along the way. Try to use the Autostrada (main highway) routes to get to Ravenna as the minor roads are slow moving and the scenery is a uninspiring.
Coming from Venice, an interesting deviation would be to take the old Via Romea down along the coast pausing at the impressive Pomposa Abbey. Fog is often a problem in the surrounding low-lying marshes with the influence of the nearby River Po.