I recently passed the October 2018 exam on my first attempt after being out of school for 8 years. I will describe what worked for me below per advice of another engineer that had recently passed.
I started going through the NCEES practice test problem by problem. For each problem, I would find the corresponding section in BOTH textbook and MDM manual. I would make sure I had an excellent understanding of the concepts, and write down the important, bold equations and more importantly made sure I had an understanding of what these equations meant and how to use them as well as pertinent text notes. I would also tab the books at this time. If I could do it all over again, I would have started with other practice tests of similar or slightly higher difficulty and saved the NCEES test for last, because that is supposedly very similar in difficulty to the real test.
I then looked at any subjects that the NCEES test didn't touch, that I thought were basic, common, and useful that they might test me on, and studied these.
I COMPLETELY IGNORED sections like reliability equations, fracture mechanics, surface fatigue, gear tooth stress analysis, AGMA methods, planetary motion, moving reference frames and LIGHTLY STUDIED things like trusses, cables, and vector equations. I also IGNORED engineering economics and ethics, knowing that I would just skip these questions if they came up and try to look them up at the end.
I also reviewed the "Plant Engineering" section of MDM and tabbed a lot of it, but didn't necessarily go in depth studying, figuring I would look for the answer in the exam if one of these came up.
I FOCUSED HIGHLY on material properties, stress/strain/fatigue calculations, body/projectile motion, friction, equilibrium equations (summing moments/forces), bolts/pins/keys, machine elements (springs, gears, brakes, belts, chains), normal distributions/std deviations. quality assurance (Cpk, Ppk, timeline mapping, quality charts).
I already had a GOOD understanding of GDT, tolerancing, and machining/inspection from industry, but I would have studied these a to reasonable depth as well if I didn't know about them already.
The exam tests breadth more so than depth of knowledge as the previous poster said. So know the basics of almost every section in the BIG THREE (shigley, statics, dynamics).
After finishing the test and all my studying, I literally went through and re-wrote all of my notes and equations and tabbed my notebook. This step was the most important for me because it helped me realize which subjects I needed to look at a little more in depth and allowed me to consolidate everything in a concise, easy to read/access format for the test. I also made notes on the units to use for the equations. UNITS ARE CRITICAL! Spend a lot of time making sure you are using the correct units with the equations and for God's sake get the "Engineering Unit Conversions" book. It is a life saver and a necessity during the test.
Finally, I simulated test day and re-took the NCEES practice test in two separate 4 hour sessions. If I could do it all over again, I would have used other practice tests for studying and took the NCEES test last. I had my wife grade the test, looked at my mistakes, and noted any common pitfalls in my notes in the relevant section so I didn't make the same mistake on test day (mostly all of them were units).
Reference Materials I Brought: Shigley Mechanical Design, Statics textbook, Dynamics Textbook, Engineering Unit Conversions, NCEES Practice Exam, MDM manual, and my notes
I wish I had time to do more practice problems, but all I did was the NCEES test. If I failed, I would have focused on problems, problems, problems. All in all, I probably did a little over 200 hours of self-studying in 2 months with no classes taken.
I hope this helped.