So how can you help?  Document what you've done and learned!  If you've got the web space, put up a web page with your project on it.  If you do that, please be sure to send me a message so I can add you to the list of examples!  If you don't have the web space, there are many places that can host you:

Web page hosting (email us if you know of other good locations.  No geocities types please)

 
arcadepinball.com - FREE Sub-Domains for the collector community (provided by MAME-HAM)
retrocactus.com - FREE Sub-Domains provided by Retrocactus.com
speedhost.com - Web hosting by the folks who host arcadecontrols.com (pay) - highly recommended  (If you use speedhost, we'd appreciate it if you mention arcadecontrols.com as a referral and let us know.  We get a discount of some sort that way)
arcadecontrols.com - As a last resort, we can host a page/pages for your projects.  However, you won't be able to logon to an account to do updating - you'll have to email changes to us, and wait for saint to get around to modifying your content.  We're willing, but we're not very fast :)  We can also scan pictures and create the html/web page if you send in a text description of it all, but that's even slower still.
** Side note **
 
The expenses of running this web site have been mounting.  The web site will always be 100% free until the day I can no longer afford it, which I don't forsee happening.  However, as this is a hobby for me I'm limited in what I can justify spending.  If this web site has been a help to you, and you would like to help with costs, there is a link on the main menu called "Donate" that takes you to a Paypal page.  If you donate, then thank you, but please don't feel obligated.  Everything here is in the spirit that makes the Internet great - people helping people spread knowledge without looking to make a buck for it.  BYOAC is just my little thank you back to the net.
With this in mind, here are some things that will help make a better write-up:

Detail

What may seem obvious to you may be stumping someone else.  If there are three steps between start and finish, please describe all three, even if step two is small.
Document as you go
The diary approach is one of the better ways of making sure you get all the details down.  Trying to reconstruct what you did after the fact is much harder than keeping an ongoing log.
Pictures, pictures, pictures!
Take plenty of pictures.  A picture really is worth a thousand words, and the more the merrier.  Take several angles.  Avoid polaroids if you can, they don't show up very well.  A regular or digital camera is best.  If you have print pictures, and no way to get them online, I'll scan them for you for free.  Also, just like keeping an ongoing log, take pictures as you go.
Got something unique?
If you have something unique, please document that part heavily :)
Remember your audience
Bear in mind that your audience is probably someone in the same shoes you were in waaaay back at the beginning of your project.  Try to think of what you wish you had known before you started, and document it.
Finally - put down the camera, put down the keyboard, pick up your dream machine, and . . .

PlayPlayPlayPlayPlayPlayPLAY!PlayPlayPlayPlayPlayPlay

Now that you've finished the step-by-step guide, hit the home button Click the home button over there on the left :) over there on the left to dive on in to the FAQ...  Good luck and enjoy!