It may have something to do with a background in improv theatre, or working now as a teacher, but here's my confession: I am not a prepper. I may, in fact, be a bit of an anti-prepper.
When I get ready to run a game, I don't have a stack of notes, flowcharts, printouts. I don't have sticky-notes attached to the sections of the rulebook I know I'm going to need. Mostly I have a handful of scrawls and - if I'm lucky - a vague map.
I don't get much enjoyment out of that kind of prep-work, I'm afraid. Haven't in years. It has something to do with time-crunch (and time-management choices), and years of reinforcement that "the way I do it" seems to work fine. Now, don't get me wrong - when I'm running a tight mystery, I still have more notes than I would for a farcical sandbox romp, but I'm still on the lighter end of GM prep. What I do enjoy is the language bit - working out NPC names that 'sound right', picking out NPC voices - and the imagery bit, thinking up descriptive phrases and turning them around in my mind for later use.
When Martin from Engine Publishing was looking for folks to review Never Unprepared: The Complete GM's Guide to Session Prep, I pinged him. "If you're looking for a review of the book from a longtime GM from the minimal-prep/anti-prep camp, I might be your guy." He kindly sent me a pdf of the book, but I feel now like the 'anti-prep' bit was over-the-top.
See, here's the thing - and it's a thing some people can't wrap their head around - there are different kinds of GM preparation. It doesn't have to be hours poring over rulebooks and drawing maps and NPC relationship diagrams and all of that, yet that's the sort of prep that gets folks to say they're "primarily improv GMs" and create this (false?) dichotomy. Even most improv-based, on-the-fly GM types are constantly doing 'prepwork' - brainstorming, recombining ideas, following scenarios to logical or illogical conclusions, envisioning set-pieces, reading for brainfuel, practicing extemporaneous description, and so forth.
In other words, the problem with the "prep problem" is the definition of "prep".
The good news is that Phil Vecchione, the author of Never Unprepared, totally gets that. Now, improv-prep (for lack of a better term), only makes up one piece of the techniques and explorations in the book, but it's given a lot more credit and leeway than most folks have bothered with. That's a good thing.
What Never Unprepared gives us is a breakdown of the stages of GM preparation, discussion of kinds of prep, and some talk about encouraging prep in a way that matches your own GMing style. As a mostly-improv guy, there were some parts I know I'll get more out of than others (brainstorming & selection, the creativity heat-mapping which I'm totally trying this week, etc). But while I read through the book, I was also thinking about a pal of mine from work who's a newbie DM for his 3.5 group. He can use every damn page in this book; not just because he's a newer GM, but because he's a computer guy who likes process and procedure and organization (a bit like Vecchione himself). And that's key - knowing who you are, your own GMing style, will go a long way toward helping you figure out what bits you can improve. It's very easy for us to evangelize the bits we're good at (I'll gladly talk your ear off about the importance of on-the-spot creativity, memorable NPCs, doing funny voices and the like), but the fact of the matter is that good GMs draw from a whole range of techniques and are willing to practice self-improvement in all categories - even the ones they don't use as much. (As I keep telling my adult students, it's wonderful to know what you're good at, but you can't leave it there.)
It makes total sense that different GM personalities will not only GM in different ways, but also prepare in different - sometimes contradictory - ways. My work-buddy is never going to be confident running his game unless he feels like he has well and truly prepared. He needs weapons at his fingertips, short-sheets, rules citations, printouts of the monsters, spare maps in case the party goes a-wandering, etc. That's his personality. Conversely, I won't feel confident running my game unless I understand the vibe of the setting, the general layout of the city, some of the cultures that I can play around with; and I want to know the NPC names and motivations ahead of time so I can flesh out personalities and voices in my mind (sadly, never on paper). I can wing NPCs on the fly, but they're never as satisfying to me. Which means I actually do prep, and I actually prefer some prep over 'pure pulling-from-the-arse on-the-fly improv'. I keep ingredients in my head instead of in a notebook, but I still prepare those ingredients to make the cooking go smoother.
Never Unprepared is good. No, it's really good. When somebody recommends Robin's Laws, I roll my eyes a little, because I didn't much care for it. But I like Never Unprepared; it's so full of good ideas and techniques that even if you don't use some of them right now, you might want them when you reread the book next year. You heard me, reread it next year. You'll change, your GMing style will change (even if only slightly), or perhaps you'll put down the game you're running now and switch to something a little different... regardless, a reexamination of your own process is in order, and Never Unprepared is a good start of that inward look. The book is an easy read with a friendly tone, you can blow through it in an afternoon. And you should, even if you're an experienced GM.
As I read through the book I kept coming upon bits where I reacted internally by thinking "this is nice, but I already know this part". But then I'd examine the point more carefully and then realize "okay, I knew that...but I'm not actually doing it in practice, am I?" I found excellent reminders of things which I know to be good-practice, but which I wasn't actually doing. The techniques in Phil's book are sound and worth looking at, regardless the GM-experience level of the reader.
Perhaps that's the crux of my favorable recommendation, then. I am an improv-heavy prep-in-the-brain GM, and have been for 25 years; I play lighter, old-school games in a semi-sandbox fashion; and I got great stuff out of Never Unprepared. And at the same time, I want to give a copy of this book to my logical, procedural, robot-brained buddy newbie GM who's running every-splat 3.5 for his rather twinky-CharOp group...because I think it will help him, as well. I still owe him some posts on on-the-fly creativity and "yes, and" principles, but the point isn't to turn him into me, or convert him from a paper-prep GM into a brain-prep GM. The purpose of any GM advice is to provide options, tools, and techniques to help each GM develop their own style, their own bag of tricks, and to build confidence. Never Unprepared can help with that.