I am not a flight instructor, but I am relatively fresh off taking the FAA Part 107 Exam (and got 93%), so I will share some thoughts and tips.
1. Many of the questions are just plain common sense, especially those relating to crew management, safety, alcohol use, and similar subjects.
2. You do not need to pay for a prep course. Read the FAA Study Guide and watch Gary Glenn and Tony Northrup's prep sessions on YouTube. I ponied up $99 for a prep course two days before my exam only to find out that the course went through the EXACT SAME INFORMATION as Mr. Glenn and Mr. Northrup.
3. Memorize those numbers! About 20% of the questions deal with the Part 107 regulations (i.e. don't fly higher than 400 feet) which consist mostly of numbers, so take some time to memorize the numbers.
4. Use the Legend. The Sectional Chart Legend that comes with the test booklet is your best friend during the exam, and its a lot easier to figure out than it looks when you see it on a YouTube video.
5. Focus prep time on sectional charts. This is a big chunk of the exam and (unlike questions such as how does alcohol affect someone?) the least intuitive, so spend a lot of time with these charts. It is also something that you will use in the field quite a bit, particularly when flying in new and unfamiliar locations.