As authors, we are constantly trying to get our names out to new people.
How else will people know we exist?
So we join Groups - search for them so that we can promote our books.
There are a few things to know before you do this.
1. Read the rules of the group. It is not wise to post a promo without knowing the rules.
For Yahoo Groups
2. Daily digest. Make sure to put email on daily digest or your inbox will run over.
3. Knowing how to make the post appealing. (I can use help with this, but the more interesting the post the more peope will read it.)
Also, there are google+ groups that you can join that allow you to promote yourself and your books.
Search for them under communities once on the correct page - there will be a place Recommendations for you. This is helpful in deciding which communities you might want to join.
There are also places like
Google Plus Pro Tips where you can learn how to use google plus.
Here is my intro to the community
Facebook also has groups you can join.
Here is one of my favorites https://www.facebook.com/groups/mfrwauthors/
As I mention in the beginning, make sure you know the rules for the groups you join and you'll have a much happier experience.
Hope this helps,