Al you are getting good advice. One thing Stanbr did not mention -- because he's so used to it by now -- is that VERY seldom do Greek roads have their Route NUMBER on roadside signs -- more often the destination. Another thing to be aware of is that your navigator, sitting shotgun, must keep his/her e yes peeled, if you are planning an exit to another road. The road signs are FIRST in Greek, and then about 200 yards onward, there's a sign in English, and then almost IMMEDIATELY, there is the exit ramp ... whew! If you are not alerted to this, you could zip right by before you react.
I think in North American we assume all drivers are a little bit A.D.D. (or maybe texting on their phones). So our highway depts "baby us." our signs start WAAY ahead -- "1 mile to Stamford exit" then "1/2 mile to stamford exit" then "1/4 mile" ... well you get it. Greece they say WHOOP -- GET OFF HERE!.
Another "funny" thing we Anglophones have to get used to ... unexplained abbreviations we don't immediately catch on to. I remember my 1st trip when 2 of us drove out of Heraklion and were told to watch for "National Road 1", which was then the # for the Biggie NOrth Highway in Crete. We kept seeing signs for "Eth 1" but thought "That can't be it!" We finally tumbled: The greek worth for NATIONAL is ETHNIKI. Duh. So keep alert to anything
Another confusing thing is that a sign may substitute a "V" in a name, for a "B". I remember looking in vain for the Church of St Barbara, and wondering who this odd unknown St. Varvara was. Duh again. A learning experience!! But FUN.