I always make good use of the airplane time by reading Travel Guides and books about my destinations. It is a great way to kill some time during the trip there, and to be prepared upon arrival.
I found that all
travel guides have small maps that are adequate for initial trip planning,
on location they fail to provide enough detail. A large map is best.
A map with
1:70.000 scale is best for specific locations (like single islands),
or a map with 1:250.000 scale for a province, would provide excellent
navigation. If you are planning to drive around Greece, don't even think
of relying on map cutouts from books and guides, unless you prefer to
around mountain roads lost for hours on end. For Greece, the "Road Edition" maps
are the best by far.
I have found that Amazon.com has the good selection of Greece travel maps, and I usually order online to plan my trip. Once in Greece, I head for the nearest bookstore or kiosk and look for maps. Several times however, I found out that it's more difficult to find good maps once on location. In Rhodes for instance, I spend many hours looking for a good map of the island (published either Road editions, or Emvelia), and in the end I had to settle for a horrible map that everyone seemed to sell for seven euro, and had so little detail I ended up not even using it.
In the last few of years I have taken along to Greece my trusty car GPS (a Nuvi 270). I bought the updated map of southern Europe in 2013 and it was very useful. The GPS did have some problems accurately pinpointing our location in smaller cities (probably due to the proximity and multitude of small streets, like in Chania), and there were some erronious directions reported inside largers cities and Athens (mainly asking us to turn into a one-way street), but overall I have been very happy and I would not travel to Greece without a GPS any more, especially when driving. For fun, we even used the Garmin on a ferry and it did a good job pinpointing the ferry's location in the ocean and even showing the nearby island names!
See detailed information about GPS in Greece.