I will tell you that you need to take at least 15 or 20 practice exams to see a good bit of questions. I took the actual NETA III exam this morning and passed. I took probably 12 practice tests, plus reviewed my results of all of my level II practice tests and was very thankful I did. I did see some new questions, but to my surprise and delight, I had already seen the majority of the same questions in the practice exams.
I recommend you review the tables regarding insulation testing of equipment, cables, and transformers. Know your insulated glove classes and color. Be familiar with arc flash boundaries and qualified employee. Read up on phase sequence relays (47), distance/impedance relays (21), and general overcurrent relays (51). They tend to like those the most.
Then just keep taking the practice exams over and over. I think this is the best study path for most. Good luck when you do take the level III exam.