Because I planned to bring my smart phone along, I purchased the electronic version of Wenk's guide. Each night, I would re-read the description of the trail I expected to cover the next day.
And while the National Geographic Map 'booklet' was my primary map, I also purchased the Guthooks JMT app. The trail is mostly very easy to follow. But there are a few places where you get near populations such as Toulumne and Red's where there are numerous cross trails, and the signs as these intersection usually indicates where each trail leads (such as a named water fall) rather than indicating which way is the JMT. So one of the pieces of advice I followed was that every time I went by a trail intersection, I fired up the app to make sure I was still on the JMT (note that when you're away from cell towers, it can take several minutes before your phone can locate its position using only GPS).
I also purchased a set of Staedtler Pens so that I could write on the waterproof Nat Geo map. I used the various colors to do things like mark my planned itinerary, number the camp sites to match Wenk's numbering system, add missing campsites. I also took one pen along with me so that I could mark where I camped each night.