Set up a route beforehand. If for some reason you have to fiddle with GPS and it's distracting, then do what people did before GPS was around: pull over and figure out your bearings.
EDIT: I don't want to come off as anti-tech in cars. I definitely believe that tech can enhance road safety, although I'm more looking forward to driverless cars. I do think that Glass is more distracting than normal GPS devices because Glass has the capability to do so much more than GPS. I don't totally trust people to only use the GPS function in Glass.
Yes, I remember rifling through a Thomas Guide on a trip up the California coast back in the day and suddenly realizing I had changed lanes. Luckily there was no one next to me at the time…
EDIT: I don't want to come off as anti-tech in cars. I definitely believe that tech can enhance road safety, although I'm more looking forward to driverless cars. I do think that Glass is more distracting than normal GPS devices because Glass has the capability to do so much more than GPS. I don't totally trust people to only use the GPS function in Glass.