I think you have to seperate the PPL flight test from real world flying. The most accurate way to locate yourself (the whole point of navigation !) is with a GPS. Frankly with the ready availabilty and very reasonable cost of modern aviation portable GPS I think anybody who does not avail themselves of this powerfull navigation tool is foolish. That doesn't mean you mindlessly follow the magenta line. Your Map should be out at all times with your thumb following along as well as a regular time/speed/distance/fuel remaining calculations. But why on earth would you not want real time position information ?
So with respect to the topic at hand if you need to divert first ask yourself what is the aim of the diversion. If it is to get to the nearest airport than the nearest function on the GPS is your first step. If it is to get around weather than the first question should be "do I really want to push on, or is it time to turn around/land". Assuming it is just an isolated area of bad weather than pick a nice obvious point to one side or the other, head for that and then when overhead turn back the same number of degrees and adjust track as required based on what you see ground to map and the GPS track guidance.
No GPS ? well then my advice is use the KISS principal. Is there a road/river/railroad going in your direction ? If Yes than follow it.