Only post advertisements to newsgroups and discussion lists which have a topic related to your website, or of significant interest to your target audience. For example, if you have a National Park Trail Guide, post it to newsgroups and discussion lists on camping, hiking, and wildlife likely to be found in the parks you cover. Don't send a message to the Wolves newsgroup unless you have a trail guide to parks near Canada. Make sure your marketing messages include your website address and a reason for people to visit. Punctuation usually breaks your link.
Some marketers suggest posting regularly.
What they don't say is that if you do, you need to post a different message. People will get annoyed if they repeatedly see the same message. If they didn't respond the first time, they certainly won't when they see it again. If you can come up with new reasons for people to visit your website, post one every few weeks, or once a month. Preferably include announcements of new content, new subjects, new ezines or discussion lists you are starting, or significant changes in the presentation of your website.