First join the discuss list by going to www.en.tldp.org and submit your proposal to this list. If you're taking over an unmaintained HOWTO, contact the former author. This may required by the copyright-license but you should do it out of courtesy even it it's not required.
These are mostly by Tim Bynum (a former HOWTO coordinator).
Be sure and use an accepted format (such as LinuxDoc :-).
Try to use meaningful structure and organization, and write clearly. Remember that many of the people reading HOWTOs do not speak English as their first language.
Make sure that all of the information is correct. I can't stress this enough. When in doubt, speculate, but make it clear that you're only guessing. I use ?? if I'm not sure.
Make sure that you are covering the most recent version of the available software.
Consider including a "FAQ" section or sections called "Common Problems" or "Trouble Shooting".
Be sure to copyright it in your name and include a license which meets the requirements stated in the LDP manifesto.
Use the standard header with title, author, and date (including a version number). See Example 3
Lastly, be prepared to receive email questions and comments from readers. How much you help people is up to you but you should make use of good suggestions and reports of errors. You may also get some "thank you for writing this" email.
After you have written the HOWTO, email the SGML source to email@example.com. Then all you need to do is to keep the HOWTO up-to date by submitting periodic updates to the same email as you used for the first edition.