Before you distribute your code to millions of potential readers there are a few things you should do.
First, be sure to spell-check your document. Most utilities that you would use to write SGML have plug-ins to perform a spell check. If not, there's always the aspell program.
Second, get someone to review your documentation for factual correctness. You can also ask for general comments. The documentation that is published by the LDP needs to be as factually correct as possible, as there are millions of Linux users that may be reading it. If you're part of a larger mailing list talking about the subject, ask others from the list to help you out.
Third, create a web site where you can distribute your documentation. This isn't required, but is helpful for people to find the original location of your document.
Using jade, or really the nsgmls command, you can validate your .sgml code against the DTD to make sure there aren't any errors.
bash$ nsgmls -s HOWTO-HOWTO.sgml
If there are no issues, you'll just get your command prompt back.
Validating XML is a touch harder than validating SGML code, but it can be done. You will need to have XML DocBook installed, and then set the SGML_CATALOG_FILES to the location of xml.soc (included with jade) and to the location of the DocBook XML catalog file.
bash$ export SGML_CATALOG_FILES=/usr/lib/sgml/declaration/xml.soc:/usr/lib/xml/catalog bash$ nsgmls -s HOWTO-HOWTO.xml