When you have planned the route then keep poring over the map and try to memorise main and easily recognised features in relationship to the route. Even go to the extent of putting a line on the map and measuring off distance and time to specific points. Overkill? Perhaps but the exercise will ensure that you have done as much as you can and the knowledge you gain will give you some more confidence.
Tip: Your route and altitude are monitored very closely and if you are even a tad off the clearance/route then you will be noted to be so. Fly as accurately as you can and show the controllers that you are able to do so. Believe me they assess your level of competence based upon what they determine and that will in turn help to determine how they process you.
Rule 1: if you are uncertain at any time, then slow down and think carefully without panic.
Rule 2: if you cannot resolve a nav problem then do not just bumble on, say so take the ignominy on the chin and ask for assistance. That's what ATC are there for, to offer a service to you.
I'd use the GPS as a linus blanket were I you, map read the whole route after extensive planning. That way you will get most benefit out of the trip and feel considerably better for it when you get it right.............and without using the GPS as well.............