I believe I've reached a definitive conclusion about the organisational structure of most 5e books. I don't know what it is about the way 5e books are put together, but I have yet to find even one that entirely makes sense to me. This isn't a complaint I make lightly, because I see how much information is trying to be delivered in these books, and it's a lot to contend with. Data's hard to organise, partly because any given human may think about structure differently, but also because a lot of it depends entirely on context. What might make sense while you're designing a dungeon isn't necessarily optimal for the busy DM looking up a specific rule during the heat of combat.
And for whatever reason, I just can't seem to comfortably find my way around these books outside of memorising their layouts. It's only fair, however, to note that this is not the case with many Pathfinder and many older D&D books. The old 3rd Edition Expedition to Castle Ravenloft adventure is so well organised it almost runs itself. And new Pathfinder books are coming out every month, and it's sometimes surprising at how friendly they are for both reading and quick reference. The 2nd Edition of Pathfinder Core Rulebook (which includes the Game Master Guide) is still relatively new, but I've challenged myself to find rules on-demand and I rarely fail to turn straight to the chapter containing the information I need, and finding the correct section is just a matter of turning a few pages.
In the 5e DMG, there are 9 chapters, and there are lots of sections within each. Try to find weather effects in the table of contents. It is there, but it's in the Wilderness Survival section. That makes sense as long as players are encountering weather in "the wilderness," but weather also happens out at sea (yes, that's technically the wilderness but in English it's generally considered distinct) and in towns and cities. It's not impossible to locate, it's just not necessarily obvious.
Traps, by contrast, aren't a subsection within the dungeon section, which is fair because traps could occur outside of a dungeon, but the Traps section is stuck at the end of the Adventure Environments chapter after Unusual Environments. And in the actual text, you go straight from airborne and waterborne vehicles to...traps? The sections aren't in alphabetical order, and not in logical order. They appear to be arbitary, and if there is a logic to it, that logic isn't communicated in the text.
Unlike the old AD&D DMG, there's no chapter titled Encounters in 5e, and the topics aren't alphabetical, so you have to read every entry of the table of contents in search of Encounters. My mind goes straight to the Running the game section, thinking that relevant tables make sense there, but actually the challenge rating budget (called XP Thresholds by Character Level) table is in the Creating Adventures chapter. I do see the logic of this one, in way: That chapter is describing how to create interesting adventures, and so it seems logical to provide the technical information for combat encounters. And yet, further information about combat encounters is provided a hundred pages later in Chapter 9.
There are no page numbers in any citation made within the DMG. For whatever reason, whenever the DMG points you to some other section, it fails to tell you the page number. For instance, this text appears on page 89:
For guidelines on generating monster-like stat blocks for an NPC, see chapter 9, "Dungeon Master's Workshop."
Chapter 9 starts on page 263. If you turn to chapter 9 page 263, you have to read through sections on ability checks, honor and sanity, fear and horror, healing, rest variants, explosives, (I'm getting to the right section, I promise), alien technology, plot twists, combat options (wouldn't this have been better in the Encounters section?), cleaving through creatures, injuries, system shock, and finally Creating a Monster on page 273.
Imagine that the DMG had just said this instead:
For guidelines on generating monster-like stat blocks for an NPC, see page 273.
I understand that it's impossible to predict page numbers dependent upon graphic layout while only writing copy. However, it's the 21st century and there's technology and publishing software now to help with that very problem.
To make matters worse, there are few visual cues to help you navigate the book. Most Pathfinder books, for instance, have a little "progress bar" along the side of each page so you know exactly what section you're in, and many are designed so you can see little coloured markers down the side of a closed book to help you turn straight to the appropriate chapter. I've tested this. It works really really well, and in fact it works so well that I've used markers to mark chapters in my D&D 5e books. I can get to the Treasure chapter of the DMG in no time at all, but only because I've marked the pages with an orange marker.
The 5e DMG does have coloured markers at the bottom right of each page. However, most are varying degrees of cool earthtones. The treasure section is the bright red exception, but they're all located at exactly the same place on the page, so it's impossible to distinguish one small section from another.
Page numbers are relatively tiny and printed at 80% or 50% gray, so it can even be difficult to quickly reference page numbers, at least at a glance.
5e books tend to fail to separate the narrative from technical data. When the DMG does present technical data, it's practically obfuscated by navigational difficulty. A book like the DMG is a great afternoon read, but it's profoundly frustrating as a reference document.
I hate to complain about something without offering a solution, and I don't want to discount the solutions already offered by the book itself.
First of all, the DMG has an index. You can look up a term and find the pages it appears on.
And of course there is the table of contents. For a very broad overview of general concepts, you can look through the table of contents and get an idea of where to start looking. You might be 200 pages off, but then again maybe what you're looking for actually is listed.
In the event that neither of those are effective, though, I sat down with the DMG and listed every table in the book. (I make an exception for the random dungeon tables in Appendix A, which I feel stands well on its own.) I deliver my table listing in three formats:
Personally, I printed the categorical version and glued it to the front inside cover. Now when I need the name of a month in the Forgotten Realms, I look in Lore and turn to the table on page 33. When I need a tavern name generator, I look in the Settlements section and turn to page 113. And so on.
As my criticism of the DMG reveal, what seems organised to one person may not be useful to another, but if you think a listing of all tables in the DMG sounds like a useful feature, then feel free to benefit from my work by downloading my list.
I hope you find them useful!