If you're like me, evocative writing doesn't exactly flow effortlessly from your mind onto the page; evocative writing requires time and thoughtful revision. Sure, you can probably produce clear & competent text, but if you're trying to publish your manuscript as a labor of love (because big bags of cash aren't waiting for us at the end of a self-publishing rainbow), why settle for mere competence? Go the extra mile and make your language great!
Here are a few pointers on how to achieve powerful writing, with an eye toward pitfalls common to modules, supplements and rulebooks:
Limit the use of passive voice
Passive voice is a sentence structure that puts the recipient of the action before the person or object performing the action. Example: "The handle was cranked by the monkey." Sometimes passive voice even omits the person or object performing the action, as in, "The handle was cranked."
Although passive voice serves as a useful tool in certain situations, many people overuse it and fall into a habit of painting incomplete or disjointed pictures with their words. Passive voice is also less concise than its opposite (active voice). For these reasons, use passive voice only when necessary. As you revise, look for places where you can switch to active voice without the eroding the utility & clarity of your descriptions.
So to revise the earlier example of passive voice into active voice, you might end up with: "The monkey cranked the handle."
For more detail on passive voice vs. active voice, and when it's best to use one over the other, check out the following articles. But keep in mind that game modules, supplements and rulebooks are akin to technical manuals, and therefore can benefit from passive voice more frequently than narrative prose.
http://en.wikipedia.org/wiki/English_passive_voice
http://writingcenter.unc.edu/resources/handouts-demos/citation/passive-voice
Limit the use of "is," "are," and other "to be" verbs
This is best shown with an example. Which of the following sounds most evocative?
1) "Three goblins are in this room. They are eating from ceramic bowl of gruel that is between them all."
2) "Three goblins kneel near a ceramic bowl of gruel, hungrily consuming their meal."
Clearly the verbs in the second sentence paint a more vivid picture. By making efforts to replace "to be" will more powerful verbs, you force yourself to think more visually, which naturally draws out other bits of detail from your imagination. You end up with a double win for surprisingly little effort.
For more information about avoiding "to be" verbs, check out the following article:
http://www.essayforum.com/grammar-usage-13/avoid-verb-5678/
Avoid "seems" and "appears"
Those two words are frequently used in gaming products as stunt doubles for "to be" verbs, and they're just as bland. You don't really need them when describing things from a PC's perspective; simply describe what "seems" to be as though it's actual fact. From the point of view of a player-DM exchange, perception is reality, and vice-versa.
Instead of, "the door seems solid," use something like, "the door holds well against the strongest shove."
And instead of, "you search, and the hallway appears safe," use something like, "you search, but gain no new information about the hallway."
Avoid the word "will"
When describing triggerable actions, "will" only functions as a space-waster. That is, you should generally prefer present tense over future tense. For example, "Pulling the lever will raise the portcullis, which will in turn alert the nearby bugbears," can be improved by simply removing the two "wills": "Pulling the lever raises the portcullis, which in turn alerts the nearby bugbears."
As another example, "The carrion crawler will attack anyone who approaches the debris," is better as, "The carrion crawler attacks anyone who approaches the debris."
Go through your whole manuscript, looking for "will," and its various contraction forms ("he'll," "they'll," etc.); I bet you can safely remove 90% of them.
Avoid explicit room emptiness
Too many modules begin room descriptions with phrases like, "This room is empty, except for (some stuff)," or, "There is nothing here other than (some stuff)." Worse, modules occasionally contradict themselves about emptiness: "This mound is empty. There is a broken sarcophagus here decorated in bas relief …" (From Barrowmaze, p. 10 – Greg, sorry for picking on you.)
Explicit emptiness wastes the reader's time. Only describe notable emptiness, such as a single empty chamber within an otherwise cluttered and overfull dungeon. If a particular emptiness begs for explicit mention despite the presence of a small number of objects, use phrases like, "A single terra cotta urn stands alone near the north wall," or, "A solitary dwarf prisoner lies on the floor, overshadowed by the vastness of the chamber."
As an adjunct, don't write keyed descriptions for completely featureless and empty rooms. Empty rooms in a module indeed serve a useful purpose; by all means, please include empty rooms on your maps! But don't give them room numbers, and don't waste words on a description that doesn't describe anything.
Don't assume the party takes all the actions
Avoid phrases that assume "the party" or "the PCs" are the ones acting in the environment: "If the party opens the chest, (bad stuff happens)," or "The trolls pursue any fleeing PCs to the entrance of the dungeon." Other dungeon dwellers (NPCs, other monsters) may open that chest or interact with those trolls, so the text ought to allow for it. Good revisions might be, "Opening the chest causes (some bad stuff)," and "The trolls pursue anyone they fight, but not beyond the entrance of the dungeon."
Eliminate pointless conditionals
"There are five saddles that can be used for flight-fungi, if the characters think of using them as flying mounts." (Demonspore, p. 56)
Wh–huh?! As written, those saddles only exist if the characters think of using them in the particular way!
More commonly, this pitfall catches writers describing the contents of chests: "If searched, the chest contains 300 gp and a potion of healing." No! This is not Schrödinger's chest! The chest contains 300 gp and the potion whether or not it's searched, so drop the "if (blah)" part of those kinds of descriptions.
Limit the description of former purposes
Avoid excessive exposition about former uses of rooms & objects, especially when the former use is no longer relevant, or impossible to discern. If the particular facts are of little/no benefit, they just waste space.
If a former purpose is important, try to imply it via trappings or other detail, without explicitly stating it. Another way to indicate a former purpose is by incorporating it into the room/area title. Good room/area titles are hard to come up with, and this technique can help you with some of that hurdle. But don't make this your default technique; unique, evocative room/area titles are generally better than always naming a room for its former purpose.
Summary
When used appropriately, these guidelines foster powerful language, and generally also reduce word count. Conciseness is important for the obvious reason: Speedy comprehension. Less obviously, conciseness reduces page count (which directly affects printing cost & final cost to the buyer and/or profit for the publisher) and simplifies the layout process. By taking the time to generate an improved linguistic product, you indirectly improve the eventual visual display of the product! More on that in a future article...
The next article covers Editing.