So...what do you do for all the campaigns and co-op missions released prior to 4.09 that don't have radio towers or broadcast beacons in them? "Just look outside the window" is great advice...when you aren't flying over water or the flat, plain, featureless steppes of Russia.
Rough navigation? Work out what distance your aircraft flies during a certain time interval. Devide the route intothese chunks. Calculate with 30, 45 and 60° angles of the flight's legs. Make a "true airspeed navigation computer" and learn how to use it.