It may just take more time and experience. If you have an opportunity to do some design/development work I'd take it. The exam is not only principles, but practice, so they'll throw stuff at you that you have to answer based on your engineering judgment alone, unless you have lots of time to search references. And, even then it's a crapshoot as to whether or not you'll find the needed information.
I'd be glad to help on any sticking points when you start studying again. I'm sure you'll pass next time.
This.
During our review course, a Process Engineeering Manager and I who have 15 and 10 years respectively were banging out answers left right and center to the plant design topic presentations. Abbreviations galore, tons of general Operations and Plant questions, and our fair share of "The One Time at Band Camp..." stories relating to operations and design aka "you cant design for stupid" when we were reviewing this outside of class. He deals with Texans, I deal with Cajuns, so it's a toss up.
In previous topics however, the young engineers were all over fugacity, Raoult's Law, and Dry Bulb v Wet Bulb, while I was still trying to figure out how to draw those lines on the tray sizing and trying to re-remember VLE curves.
Even then, it's not a cakewalk. This past exam was full of plant design questions on...Distillation. I have NO CLUE about that as I do upstream work, but I could get a bit of a handle on it. A simple question on packing materials would have been really easy for the refinery kids, meanwhile I had to check and make sure that "M&Ms" were not an acceptable material to use in a stripping column.
While I'm positive you cant study for it, you CAN make you life a lot easier by tabbing properly. The above-referenced manager and I are going to try to help out that AIChE class we did (the teachers are all volunteers) and "pay it forward" with "Useful Tabs to have in Perrys, and why they will help" topics.