You can subscribe to the following mailing lists:
First is <discuss@en.tldp.org>, which is the main discussion group of the LDP.
Another is the <docbook@en.tldp.org> list, which is for questions about DocBook use including markup and transformations. If you run into trouble with a particular markup tag, you can send your question here for answers.
You can subscribe to either list by sending a request message to either <discuss-subscribe@en.tldp.org> or <docbook-subscribe@en.tldp.org>. The subject of your message should read "subscribe" (no quotes). To remove yourself from the list, send an E-mail with the subject of "unsubscribe" to <discuss-unsubscribe@en.tldp.org> or <docbook-unsubscribe@en.tldp.org>.
If you are interested in DocBook beyond the simple markup of your LDP document, you may want to consider joining one of the OASIS DocBook mailing lists. Please see http://docbook.org/mailinglist/index.html for more information.