There are quite a number of things that will drive me nuts whenever I look at a published adventure. Whenever I see those things, I immediately think that the author is trying to beef up his word count. I have held myself on this side of going full rant, though there is some ranting here in. See for yourself whether this warrant the rant tag.
5- Passive voice
The room has already been plundered by bandit or The animals have all been chased away from the castle. The passive tense is acceptable when making something lyrical or prosaic. Adventures are neither.
Always think of the GM when he has a table full of players bombarding him with questions about this or that. Finding what you are looking is quicker with simpler language.
4- Boxed Text duplicating maps
This is something I have grown to be much more annoyed by, particularly with PFS. Room descriptions that end up with a long paragraph describing where the door are (and the doors rarely matter to the adventure anyway).
Describe what is important and let the GM run the game.
3- "Nor Crystal Falls"-syndrome
VTF3-01 Nor Crystal Falls was a Living Greyhawk adventure, the first of our meta-region (the Velverdyva/ Tuflik/ Fals trade route, occupying the western routes of Greyhawk and the Baklunish West). The adventure was fine, when I played it, it went pretty much like this: "You are in this Crystal Tower. You enter a room, there is a priestess of water there, roll initiative. You enter another similar room, another priestess or water, initiative." I thought it really sucked as an adventure.
Then I read the adventure and prepared to run it. WOW. This adventure had a lot of flavorful background on EVERYONE of these NPCs, about half a page IIRC detailing why they joined the cult, who they liked, who they disliked, etc. All this background was nothing more than garbage and junk. It was useless and though I wanted to try and share it during the adventure, players rightfully understood that killing priest of Elemental Evil/ Tharizdun was a much safer option...
So all this writing was just junk, too bad because there was adventure potential there, and it would turn the adventure from a three-part combat into something more.
This adventure has really molded me as an adventure writer: anything that's not essential to the adventure, leave it out. This is something I later learned was called "Chekhov's Gun". I wasted so much time reading and thinking how to portray these cultists, when it would've been much more rewarding to merely have them charge across the room brandishing their weapons.
2- The Novelist
Adventures are not the place to showcase your wordsmithing skills. Keep the flowery text to a minimum. It is fine to provide some neat prose, but keep boxed text to an absolute minimum.
Beyond the introduction/conclusion, no boxed text should *EVER* tell the PCs how they think or feel about something. Even passing comments like "The biggest man you ever saw" are fine in fiction, but in RPGs... Provide a reference "as tall as a bear" or "smaller than a lap dog" gives reference without assuming of the PCs' experience.
Next in this section... Do not for the PCs into a course of action. "You meet with the king who offers you a post, which you accept." NOOOOOOOOOOOOOOOOOOOOOOOOOOOOO. NO. NO. NO. A simple test for this is to assume the following: I play a character who always says no to everyone and everything (such a character being a complete jerk, and be unplayable, but is perfect for the purpose of the exercise). If that person would immediately start screaming "NO WAY! I'm not doing that!" Then change your text.
Finally, do not write whole pages of boxed text, broken only with "give the PCs a chance to agree."
Oh and Braziers are not Brassiere...
1- Future tense
This one share a number of points with passive tense. It is rarely found in boxed text but all too common in GM-text.
After defeating the monsters, the PCs will find a map. They will follow the clues to the treasure. This is one of those things that once you notice, it becomes EXTREMELY annoying, almost like it is trying to assault me, punching me in the face. This one really makes it hard to find important words in a paragraph because "will" appears every sentence and our brains love to find repetition and pattern.
Write your adventure in the present, active tense. It will make for a lighter, faster, more dynamic read and facilitate the GM's job when players are in his face asking for the color of the African swallow.