There have been a few requests for this thread, and the part I compiled, so I am reposting it alone for reference, with an alteration for new info the editors put up. I hope this helps potential contributors.
Tips for Potential Dungeon Contributors
*PUT YOUR NAME AT THE TOP OF YOUR MANUSCRIPT - Put your name at the top of the first page of the manuscript. Submissions usually get printed out, and if we have to go back to your email, figure out who sent what, and write your name at the top of your manuscript, you are making the staff do unnecessary work.
*ONE SUBMISSION=ONE EMAIL: This is far eaiser to organize for the editors.
*INCLUDE THE SDF FORM AS A SEPARATE FILE - It makes filing a lot easier if you attach the SDF form as a separate file. We can't accept an adventure without an SDF! It may be sent in paper form or emailed in electronic form.
*DON'T JUST PASTE YOUR QUERY IN THE EMAIL BODY - Your full query should be in the word processing format you will write the adventure with, preferably Microsoft Word.
*PROOFREAD - A spellchecker will make minor fixes, but an abundance of grammatical and spelling errors makes your manuscript much less attractive and professional looking. Try to get others to read it first for clarity and correctness. Give yourself time to adequately go over the whole manuscript. This can be especially important for foreign-language contributors who must compete with native speakers. Also, learn how to use apostrophes.
*SHOW, DON'T TELL - Instead of saying "a really cool trap" or "a mind-bending puzzle", give us a QUICK idea of what it involves. Additionally, minimize backstory and NPC information for the sake of increased description of what will actually transpire in the adventure. You do not have to include every single monster or grunt, but the main NPCs and villains need to be have some detail. Also, include notes for anything particularly unusual.
*TWO PAGES MAXIMUM PER QUERY - Two pages can seem limiting, but it's extremely important to get as much of the adventure itself into the query as possible. When possible, condense or sacrifice background description in favor of telling us about PC involvement. If you can't explain your adventure in two pages, it's probably too complex to fit into one of our adventure slots in the magazine. If we like your basic idea but think we need a longer proposal, we'll ask for it.
*DO NOT RE-SEND QUERIES - Please don't resend a query unless we ask you to rewrite it for us or we ask you to resend it because we did not get it.
*BE PATIENT - It can take some time to get a response. The average time between proposal acceptance and manuscript submission is a couple of months - even the best queries generally have some changes that need to be made, and the editors understand that such things don't always happen overnight.
*DO NOT PRESUME PC ACTIONS - The whole reason we like D&D is because it allows us as players to do anything we want. In your adventure, don't presume that the PCs are always going to follow the path you've laid out. Go ahead and talk about incentives for PCs to take various actions, but realize that being lead by the nose is rarely fun or effective.
* PUT YOUR BEST FACE FORWARD - Consider what elements make your proposal exciting and a "must buy" from an editor's perspective (great story, great NPCs, great location, basically great anything) and put them up front. Let us know what makes your adventure cool, because if we have to go hunting for it, there's a good chance it's going to get missed.
*WE ARE NOT YOUR PLAYERS - A lot of authors like to be sneaky about key plot elements, avoiding a big "reveal." Even if the adventure is a mystery, it shouldn't be mysterious to us. Don't hide elements of your adventure from us. Give us all the information we need to make an informed decision about whether or not to buy the module. If you don't, we're probably not going to buy it.
*WE NEED MANY DIFFERENT KINDS OF ADVENTURES - We still need Eberron and FR adventures. We need low-level adventures. This changes around a lot as months go by, but right now we're seriously hurting for good low-level proposals.
*AVOID OVERUSE OF THE DUNGEON CRAWL
There will always be a place for "traditional" dungeon crawls in Dungeon (it is, after all, the name of the magazine), but we're beginning to yearn for more interesting adventures.
*NO MORE BORG ADVENTURES - At least five proposals from the current meeting (and this is after scores have already been rejected) hinged on some sort of creature, usually something that looks like a bug, trying to spread out and assimilate innocent folks.
*MORE URBAN ADVENTURES - This ties into the request for more than just dungeon crawls, but we're really interested in some cool urban adventures that can be easily slotted into any urban D&D campaign. City adventures, like any other adventure, should generally be for the core D&D world. If you want to do a city adventure set in Forgotten Realms or Eberron, make sure that it's in the city you chose for a reason. In the end, there's no real difference between the two as regards a footprint in the magazine, since we'll want to present enough info in the magazine to run the city even if it's been extensively detailed elsewhere. For an excellent example on how to structure and present an urban adventure, check out "The Styes" in issue #121.
*READ RECENT ISSUE OF DUNGEON - Not only will this help in showing you what kind of adventures we tend to accept, but it'll also tell you what adventures we've run too often.
*TAKE YOUR TIME - Once we accept a proposal, we typically give the author several months to write the manuscript. Usually three months. We never expect a writer to be able to generate a full manuscript in a week.
*MAPS MUST BE CLEAR - If you can't draw good maps, do your best to at least draw a clear and legible map. Don't clutter it with too many notes. Don't do it in pencil and then photocopy it so it's hard to read. As long as it's understandable, you should be fine.
* YOU CAN USE NON-CORE BOOKS - You're welcome to utilize concepts and rules you find in any book published by WotC, but keep in mind that we'll need to reprint enough of the rules so that someone without the book in question can still use the adventure.
*USE THE NEW STAT BLOCK - Don't go getting tricky with text boxes or frames or adding lines. We take care of the actual document formatting during layout. Just presenting the stat block in plain text is all we're looking for, like this:
MONSTER NAME CR XXX
Gender race class level
AL Size type (subtype)
Source xxx
Init xxx; Senses Listen +xxx, Spot +xxx
Aura xxx
Languages xxx
AC xxx, touch xxx, flat-footed xxx
hp xxx (xxx HD); regeneration/fast healing ; DR xxx
Immune xxx
Resist xxx; SR xxx
Fort +xxx, Ref +xxx, Will +xxx
Weakness xxx
Spd xxx ft.
Melee weapon +xxx (xxx)
Ranged weapon +xxx (xxx)
Space xxx; Reach xxx
Base Atk +xxx; Grp +xxx
Atk Options xxx
Special Atk xxx
Combat Gear xxx
Spells Prepared (CL th):
2nd-xxx, xxx
1st-xxx, xxx
Spell-Like Abilities (CL th):
1/day-xxx
Abilities Str xxx, Dex xxx, Con xxx, Int xxx, Wis xxx, Cha xxx
SQ xxx
Feats xxx
Skills xxx
Possessions xxx
*A FEW SMALL DETAILS - I think it's time to lift the "double-spaced" restriction from proposals; there's no need for this. Another thing that needs to go away: using 2 spaces after the end of every sentence. Please only use 1 space after that period.
*One space after each period -- not two.