Since there is no magnetic field compass is out. No GPS satellites either. I guess some old school methods could be used but I see some potential problems.
Assume we are over the cloud tops, can we actually see the night sky as clearly as on earth, e.g. if we look at stars for navigation?
There is no moon to use as a reference point. Will that cause problems navigating using say a sextant?
How about the length of the Venus day at 243 earth days, would that cause any kind of problems? You can't exactly wait for noon and check the hight of the sun.
I speculated whether you can use fixed points on the surface, but with the thick clouds and atmosphere I guess you can't really see the surface anyway. Say you are 50 km above surface are there simply ways of "looking" at the surface whether by radar, infrared, sound or whatever?