Make a commitment.
This exam is no walk in the park. It requires a significant investment of time and energy. If you decide to pursue it, give it your all! Dabbling can easily lead to frustration, and be very costly.
Take the hardest section first.
The first exam you pass is the only one you aren't "on the clock" to pass. You can retake it as many times as you need to at any pace you'd like. Of course, "hardest" is relative to each person, so I suggest taking some practice exams to determine your weakest subject.
Have a plan.
Once you pass a section, put together a detailed plan of when to take each remaining section allowing for retakes. 18 months may seem like a lot, but there are only 6 testing windows in 18 months, so your oppertunities to retest are not infinite. I suggest taking 2 sections per testing window as this will allow 1 1/2 months of study time for each section while allowing plenty of time for retests.
Retake failed sections ASAP.
If you fail a section, retake it before any other sections if at all possible. This will allow you to maximize the benefit from the studying you've already done.
Schedule early.
Set your appointment as soon as you get your NTS. You can reschedule for free as long as it's more than 30 days away from the test date. Scheduling early gives you more flexibility if you need to change your plan to accomodate a retest or other factors (family, illness, work, etc.)
When in doubt, MCQ!
If you are short on time to study, or simply feel overwhelmed and don't know where to start, practice multiple choice questions are always a good option. After all, MCQ is the majority of your score for every section. To maximize benefit, make sure you understand why you got each question wrong/right.
Take breaks.
Studying continuously for hours on end is less productive than studying for a few hours per night with breaks. Start studying early so you don't have to cram at the end.
Read questions carefully
The exam is grueling, and the questions are often complex. It is easy to get exhausted or anxious and misread a question, so take a few breaths and read carefully.
If anyone else has some helpful tips to share, please feel free!